I do a ton of equestrian photography.
I use a pair of 7D's for the vast majority of it (90% or more). Those have essentially the same sensor and high ISO capability as your 60D, just a slightly more sophisticated (but no more sensitive) auto focus system and higher frame rate. I do also have a 5D Mark II that's proven useful at times in lower light situations, but I use it far less than the crop cameras. The 5DII can do about one stop higher ISO than 7D (a 6D offers slightly higher ISO than 5DII, as well as extra low light focusing capability).
Primarily, I'd rather have the "extra reach" of crop cameras than the high ISO capabilities of full frame. My most used lenses are 70-200/2.8 IS, 70-200/4 IS, 300/2.8 IS and 300/4 IS. I also carry and sometimes use 28-135 IS, 10-22mm, 24-70/2.8 and a number of shorter primes (portrait, macro, tilt-shift).
In order to have the "reach" of a 300mm lens on crop camera, with a full frame camera I'd have to lug around a 500mm. No thanks!
But in general it's more down to lenses than the camera they are used upon...
What lenses and cameras I use depends on the type of event I'm shooting, whether or not I can be or want to be mobile, whether or not an arena is covered, if I'm not working outdoors.
For dressage, I often have to work in covered arenas. But I am not mobile at dressage events, so I can set up a 300/2.8 on a tripod to reach the other end of the arena and use a 70-200/2.8 for closer shots. I prefer to to stop down a bit for adequate depth of field when I can, but like to have f2.8 available if needed to get shots in darker areas of the arena. Generally speaking, unless at a very high level, dressage cannot and should not be photographed with flash. Most junior and amateur dressage riders and horses are not accustomed to flash. Dressage is slower moving than some other events, so I can get by with a slower shutter speed in many cases... 1/250 and 1/320 is sometimes possible.
Hunter/jumper, stock competition, gymkhana and English/Western are types of events where I need to be more mobile and tend to use 300/4 IS and 70-200/4 IS for mostly handheld shooting. These types of events are sometimes in covered arenas, but often are in open, uncovered venues. Even if the arena is covered, it's quite likely to be well lit. It is possible to use fill flash judiciously, but I try to avoid it as much as possible, and never use it too close.
Hunter/jumper, arena jumping, gymkhana and all sorts of stock competition tend to be moving, so I need to use 1/640 or faster shutter speeds, if I want to freeze the action.
For trail trials I try to carry minimal gear because I'm walking the trail with the horses and riders (not the entire 6 to 10 miles of most TT courses), but it's entirely outdoors in good light. I mostly use 28-135 on one camera and 300/4 IS on another. I have had trouble with the noise of 5DII in the quieter settings of trail trials, but not with 7D or even using 5DII in noiser arenas (I know the 6D and 5DIII have "quiet" modes, but haven't used them, so can't be certain how effective they are or if there are other issues using them.)
Cross country is one type of event where I always struggle to figure out what to carry. If I working close to home or have a ride out onto the course, I might take larger lenses and tripods. But if I'm hiking, I'll opt for the lighter stuff.
I sometimes use the full frame 5DII for planned, stationary portraits (after testing to see if the horse reacts to the shutter noise). I also will occasionally use it in particularly dark venues. But generally even those I can find brighter spots and work those with my 7D's instead. So I might only be limited from shooting in particular portions of the arena.
If I could only carry one, it would probably be a crop sensor camera... on a budget 60D or 70D, 7Ds have been working well for me for over 4 years and upwards of 100,000 clicks apiece, and probably will get replaced with 7D Mark II's when those come available. (In the past I extensively used 50D, 30D and 10D, too.) A crop camera gives the most versatility and flexibility, IMO. It offers the "extra reach" that allows smaller, ligher, less expensive lenses to serve, plus all lenses both EF and EF-S can be used (a full frame camera is slightly limited, to EF only).
But, sure, 6D's low light capabilities could be nice at times. It's probably a good two stops higher ISO capable than your 60D or my 7Ds... and it's AF is able to focus in about two stops lower light, too (-3EV, compared to -1EV). Note that the 6D would be limited largely to center AF point only, for any AI Servo/action shooting and low light. (That woudl be fine by me... smae is true of my 5DII and even with 7Ds and 50Ds, which have much more capable peripheral AF points, I still only use the center one most of the time.)
Hope this helps!
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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