It's a rabbit hole. Best to stop looking while you're ahead I always find a good deal on an older model. Then I see one that is a version newer for a couple hundred more. The cycle continues until I get to "just a little more and I can get a 1DX". I'd start with what you think you would like in a body. Then read the reviews here on the site for that model as well as the next version to see what had changed if anything important to your needs. Higher iso (like 3200) is great for me, but maybe not necessarily for you, so an older model might be just the ticket. Software might help pull out details in those shots too if only 1600iso is available.