Nick what do you shoot more specifically than wildlife..........that's the biggy here do you need the high frames per second do you constantly shoot crepuscular beaties. Mate I started with a 550D is a cracking little camera. i've never used the 7D have a dig for a guy called Daniel Cadeaux (hope the spelling is right) he was a 7D user produced some stunning images, with that camera!! It seems from reading his posts way back that ETTR will be a big player with that camera. Mate I went from the 550 to the 1div ,
MPB have some in stock circa £550 might be too much also might be worth the wait. You might find cheeper privately. It's a hell of an upgrade even though I still am blown away by that little 550. It was primarily the need to drive AF fast plus that frame rate that appealed to me. Plus it is built like a tank. so anything the UK throws at you ,you should be good weather wise. Which is always important with any UK wildlife photography: one is gonna get half drowned in this country at some stage it a given
Tailor what you buy to your needs mate .......................you personally , might not like the weight of a 1 series body, tis a lump. It's a tool Nick.......... buy the best one you can afford to fit into the type of wildlife you love shooting most. Mate the 1div was four thousand pounds or there abouts when new under £600 represents one hell of a tool for wildlife image making.. I'd get me head down and save a bit more .
I can't provide you with anything constructive on other cameras I've only used three DLSR's full stop. i'm no tech head
I only know this little bit
..going from a 550D to a 1Div is a tiny bit mind blowing
. That jump wont make you a better tog. But it will allow you to make images far more reliably than you can in certain situations because of the more advanced AF and the speed of it. it will allow you all the focal points to compose if there is time or close. it can be flipped effortlessly it's a pro camera to shoot wildlife a few years back. Modern sensors are better in low light more advances in AF but only incrementally better. A 1div is a really really good tool for the money right now.
I repeat best tool for you not me
see if you can find someone local and try some bodies Nick, you need them in your hand. We are all different the weight and size of a canon one series could have huge implications for some of us,it's not just about pixies and AF speed and iso performance you have to be able to maul this stuff to your subject to some level or other ..
stu