I'll make the bet it's 5D4 since its AF gets you shots you otherwise might miss and a missed shot at 50 MPs isn't much good. That would be assuming you're not dealing with very static birds, otherwise it's 5DSr - Alan am I close? 
Jack
Jack
Act444 said:5D4 vs. 5DSR...
5D4 wins on speed and high ISO...
5DS R wins on resolving power, reach and sharpness...
I'll say this, there's just nothing quite like a 5DSR shot razor-sharp at 100% view!
That said, personally I've been using the 5D3 and 5D4 a lot more lately mainly due to shooting environments.
Mikehit said:That's very interesting, Alan.
Are you able to offer some thoughts between the 7D2 and the 5D4, particularly regards cropping in low light. I realise the 7D2 has better resolution in good light but I was thinking how the pixel quality offers any advantages at (for example) 1600 and above.
I still consider my 6d my high ISO go to camera over my 5d IV. Don't get me wrong the 5D rocks, but 3200 and up the 6d shows it's worth and has smaller file size to boot. Both focus very well in low light, both smoke my 1ds mkiII in this regard.bholliman said:keithcooper said:For someone using the 5Ds regularly and appreciating those extra pixels, an example at 12800 ISO somewhat misses the point
I do sometimes push it to 800, whereas my 1Ds3 sometimes got used at 400 and my 1Ds at 200 ;-)
I try to use my 6D for situations where I need higher ISO, but at times do use my 5DsR in poor light. I've been reasonably happy with 5DsR images at up to 3200 ISO with heavy noise reduction and downsizing. If I owned a 1Dx (Mk1 or 2) or 5D MkIV, those would be my preference for low light/high ISO.