Before you rush into full frame, have you compared, say, a 7D with a 5DII? I did recently and made some 15x10in prints for direct comparison. They were virtually identical and I was the only member of my family that could tell them apart, and I got it wrong once or twice! Unless you print very big most of the time, you will not see any benefit from full frame. If you don't believe me, try it. There is a difference of course, but it is extremely subtle.
Against that, full frame is bigger, heavier (it's the the lenses) and a lot more money. Crop format works out better all round, especially with some of the high grade EF-S lenses (10-22, 17-55 2.8) that really make the most of the smaller format at shorter focal lengths (there's very little benefit to making longer EF-S lenses, which is why Canon doesn't bother, or Nikon for that matter).
In addition, the 7D is a far better wildlife and action camera than a 5DII. Better AF, faster frame rate and of course much more effective reach. 70-200 lens on full frame is frankly hopeless for wildlife - you'll be needing some £5k primes. Even on a 7D you need something like the 100-400L to have a serious go. Extenders won't get you anywhere.
I'm not trying to talk you out of full frame, just trying to make you aware of the differences which might not be where you expect them to be. I would like a full frame kit myself, but only in addition to my crop cameras; if I had to choose just one, for a range of subjects similar to yours, it's crop comes out top and it's not just about money.
