Tommydigi wrote in post #19405762
I've also been debating keeping my R and getting the R7 or selling my R and getting an R5. Overall I'm pretty happy with the R but I do like the idea of 1 camera that can do it all. Going to hold off until later in the year but I'm leaning heavily toward selling my R and 7d2 and getting the R5.
Do this instead: Keep the R for landscapes/low light/slow moving work. The sensor size matters for that stuff.
For birds/wildlife: Get the R7
Now you have TWO cameras, both specialized, and you will have saved yourself roughly $900 or more, depending upon how you do the comparison. Also take into account if you do or do not need the spendier cards/card readers...
Thing is: Full frame + Birds does require longer focal lengths, which, yes, can be had, but - I'd argue that it's much easier/cheaper to cover that gap using the crop sensor > the bigger/often more expensive lens. Sort of 2 paths to get to the same result...
You mileage may vary!! I def DID miss the crop factor for birds in most cases utilizing the full frame... it then becomes a question of: How does one make up for this? What lens and at what costs/compromises? FOR ME: I like the lighter 100-400II with its insane IS, on a crop sensor like the 90d vs. having a heavy front element on a tamron/sigma while using a full frame and maybe an extender. I tried that on a canon 5dmkiv + 1.4xiii for a year... keeper rate increased by going to a "stupid" 70d and bare 100-400ii. I got A LOT Of flac/backtalking by bringing that up online however... 
Birding on full frame in my book, becomes kind of a $$$$ game. Are you making money from your work? Could you do just as well with a cheaper body like the R7? Are you really going to need an F4/big white to get the shots you want? How is your approach game?
Those are just some questions among many.
For me personally: I used to always have one crop sensor on a telephoto, and another full frame on the tripod doing a time lapse, this way, you have the best of both worlds. Maybe you end up occasionally doing some lower light bird action and you utilize a hide, or you're dealing with owls or species that allow you to simply be closer, and that will work great on a full frame situation. being that you're in Chicago, I'm guessing you may need the lower light full frame performance more so than say - someone snowbirding it to arizona and getting birds in great light virtually year round. Having done birds in Oregon, I def. understand the idea behind a full frame, BUT, some birds you can totally get away with overcast/evening light and go hand held at 1/50th or slower for a perched great horned owl. So, I guess it depends on what bird photos you sort of envision??? Personally I do a ton of thinking about what shots I want FIRST, and then, I go find them.
Sometimes working backwards is the way to go:
What birds?
Where?
behavior/action?
What kind of light?
Forget the camera completely - pretend you're a painter instead!!
Just know that you DO pay a premium for the one camera that "does it all..." I am going to the "R" only because - we have close to ZERO Birds here where I live... and on the 'one off' situation, I have my highly highly highly under rated 90d - it's like the pesky/annoying mosquito of cameras that pisses people off - I sort of like it for that very reason 

