need some honest(non fanboy) advice.

[RTfuture]

So I've finnaly got the funds saved to upgrade my camera body. I've had a 60d for the last 4 years, and excited to make the step up.
I have £2,000(UK) Which is just enough to buy a 5D MKiii. OR a 7d MKii with £500 to spare... Which I would put back in to go towards some glass etc etc.

I've looked at endless comparisons, and still feel no closer to a decision. In terms of what I need in a camera.
The money I make from photography is very low light work. I shoot at ISO 2500 regularly, and can't push the 60d any further. So good low light performance is a must.
However, I'm starting to do more portrait work also, and have one eye on the future.
From what I've seen, the 7d looks like i'd get more for my money. But not sure if I want another APS-C. Does this REALLY matter though?! Please... Any further clarity will help!

Thank you.

www.remember the future.co.uk

[RobertTheFat]

Last year I bought a 5D3 to go with my two 7D's (Mark I). I've been surprised at the difference in image quality and low-light performance. The 5D3 is significantly more accurate in its automatic white balance. I'm not sure how much better it is in low light, because I don't like to turn the ISO up any higher than necessary. But I've used it at ISO 2000 (and I think also 2500) with no apparent noise.

I don't doubt that the 7D2 is a very fine camera, and I'm sure I'd want one if I hadn't decided to make the jump to full-frame. One drawback to APS-C that Canon seems unwilling to address is that its best lenses don't come in focal lengths that most people would consider ideal matches for that format. One could argue that that's a subjective judgement, but what constitutes a "normal" lens for a given format does have some objective basis in the optics of the human eye. But is FF worth an extra £500? I can't make that call for you; all I can say is that the 5D3 was worth the extra money to me.

[ebiggs1]

With no more than what you stated, 5D Mk III is the choice.

[TCampbell]

I would agree that based on what you've described, the 5D III is the better option.

The 7D II is optimized for action photography.  What it has over the other models in the price range is it's extremely fast shooting speed (it's not just the shooting speed... it's the focus system, the buffer size, the rate at which it can write data to the cards, etc.  It's all optimized for speed.)

The 5D III was a bit of a departure from the 5D II in that I would not consider a 5D II for serious sports... the focus system was simple.  The shutter speed wasn't particularly fast, etc.  But what the 5D II had over most other models was it's full-frame sensor and extremely good ISO performance.  The 5D III improved on that -- providing even better ISO performance... but then also made massive improvements in the focus system and buffer size.  You actually can use a 5D III for sports (something you probably would not have done with a 5D II).

Given you indicate you're mostly shooting at ISO 2500 and need good low-light performance, the 5D III is going to provide more low-light perormance than a 7D II.  The 7D II is significantly improved over the 7D classic, but it's still not going to compete with the 5D III in that area.  High ISO with low noise is one of the things the 5D III does best.

You also mentioned portraits.  If you like the blurred background you can create with a shallow depth of field, a full-frame camera is going to do this better than an APS-C camera.    If you shoot with both cameras using the same lens focal length, same distance, and same f-stop, then you have to multiple the f-stop by the crop factor of the camera (in the case of an APS-C sensor that's 1.6) to arrive at the effective f-stop for purposes of depth of field.   If you shot with f/2.8 on both cameras, then you'd have to multiply the 2.8 x 1.6 = 4.48.  That means even at f/2.8 you'll give the depth of field resembling what the full-frame camera would have provided if you had shot at f/4.5.    This isn't camera model specific... it's a comparison of sensor sizes.   It's the reason camera phones (or any camera with a tiny sensor) can't seem to generate any decent background blur -- the crop factor is too high (so it's as though you're always shooting at a very high f-stop.)

You've just mentioned the two needs... ISO & Portraits.  Based on just those two factors, the 5D III is the camera for you (but then based on just those two factors, a 6D would also be an option).  There may be other factors that you've not mentioned that would casue me to change my recommendation.

[f64]

Of the two the 5D3 will give you a better image. Since its FF you can shoot at a lower ISO, given all identical parameters, to the 7D2 since more pics are there to absorb light. If you shoot at the same ISO you'll get less noise in the dark areas. http://www.dpreview.com/forums/post/55498672 

On the other hand your lenses won't have the same reach that they had with the 60D. It might be a tough choice. Would you rather have the best best image or a better image and more updated options. Since the 5D3 is 3 years old right now there are some great deals out there.

[ebiggs1]

"... since more pics are there to absorb light."

Of course you know this is incorrect?  You meant to say larger pixels (pics?) absorb more light.  It is the size that matters not the quanty.

[f64]

Yes, you are correct. The pic size (6.25 micron sq for the 5D3 vs 4.1 micron sq for the 7D2) is what should give the 5D3 the edge transfering light. I haven't shot ASP-C for some time now, only FF. I do remember it was the noise level at high ISO with the smaller sensor that pushed me to FF. What I find odd is based on published specs the EV and DR seem to be the same for both bodies?

[TCampbell]

Ev deals with the focus system.  Canon publishes a focus "working range" which is an indicator of how much light the camera needs to be able to focus a shot.  But the focus sensors are on the floor of the camera's mirror chamber (just below the reflex mirror.)

Dynamic range deals with the "well depth" of the sensor -- and that's different than the photo-site size in microns.  

You can think of each "photo site" as a long skinny tube which holds drops of water (but it's really storing photon count).  Imagine my tubes can each hold 50 drops of water before they are "full".  Once full... they simply overflow.  If I try to put 40 drops of water in some, 50 in others, and 60 in a few others then I can tell which "tubes" had 40 drops... but I can't tell which ones had 50 vs 60... because regardless... they're all just "full".  But suppose I use longer (deeper) "tubes"... maybe these better tubes can hold 100 drops of water.  NOW... I can tell which tubes had 40 drops... which had 50... and which had 60.  None of them over-flowed.  That's the concept of "well depth" of an imaging sensor and that's how you get dynamic range.

Dynamic range will not be an indicator of ISO performance or noise -- it's another factor entirely.

[f64]

Thank you

[RTfuture]

Thanks to you all! More helpful on here than most reviews I read/watch. But I suppose them reviews don't cater to my needs.
I can't believe the 5d MKiii is still so high priced 3 years later. But then I suppose that speaks volumes for its quality. I really want FF now I think. Although I will be losing one of my EF-S lenses. Which I'm not overly fussed about. I may take a look at the 6d too.
Thanks again!