Nicer lens or 2 lenses?

[nistor]

I have an R8 RF 28-70 2.8 and an EF 85 1.2ii. Picking up a longer lens for full field soccer and to try my hand at birding. Choice is the RF 100-500 which would be perfect, or the EF 100-400ii which would allow me to also pick up the RF 70-200 f4. I think the extra 100mm will be really helpful for birding plus I could add a 1.4 tc eventually if I like it) but my primary use will be my kids soccer games. I’m having a real tough time deciding.

[shadowsports]

Greetings 

I can see your conundrum.  One consideration.  Shooting full field soccer from a single vantage point regardless of the lens will be challenging.  The RF 70-200 f4 and moving (foot zoom) would likely prove most effective.  

TC's: I own the RF 1.4x version.  It can be used on the RF 100-500 between 300-500mm only.  It cannot be used on the RF 70-200 f4 at all.  It's only compatible with the RF 70-200 f2.8 Z series which blows your budget.  I would not buy an EF version for one lens.  (If you were thinking about it?).  Putting it, an adapter and a moderately heavy lens on the front of an R8 might be slightly unwieldy.  Have you considered selling your 85 f1.2 to offset capital expense?  I know it's a beautiful lens. 

For sports and birds, my recommendation is that you opt for the RF 70-200 f4, sell the 85 f1.2 and buy the RF 100-500 and 1.4TC when practical. I purchased my 1.4X TC refurb directly from Canon and saved a boat load.  It's out of stock now but it'll come back. 

Shop Canon Refurbished Extender RF1.4x | Canon U.S.A., Inc. https://share.google/BtsZD25z3f9wWO1SM

Since it's winter time, the urgency for a birding lens and TC is slightly less.  

Let's see what others say 🙂