It all depends on the light!
I'll explain. I've got a 7D and what you gain in crop factor magnification (thus saving you a lot of money on lenses) you lose in image quality. On the 7D it's very, very hard to get tack sharp images because your starting point is pretty much like you're always using a digital zoom at 1.6x magnification on a full frame camera. This difference in image quality caused by the lack of sensor size and quality (compared to a 5D MkII and a 5D MkIII) is immense in the real world. The guy I sit beside at work brought in his new 5DMkIII and image quality is simply in a different league.
Now, I mentioned light. I live in the UK where intense sunlight is not the most common type of weather that we see. This means that fast glass is hugely important, the weather also means that our wildlife sits in lush green fields or leaf laden trees and thus getting decent shots with sharp contrast is also really hard work. So, when you consider that the 7D autofocus uses colour information as well as contrast in its processing then I am certainly figuring out why I'm finding it hard to get crisp shots.
The low intensity of light in the uk means I have to use prime lenses (oh what a shame i hear you cry) but this means that i've got very little depth of field to play with and thus I get the beak of a Kestrel in focus but the tail is in a world of Bokeh. This obviously means I have to stop up the aperture but without the light intensity I'm forced to up the ISO to maintain shutter speed. It is in doing this that the difference really starts to show. The sensor of the 5D's are so much better that the raising of the ISO has almost no effect on image quality.
Comparing my 7D with both of the 5D's in good (but not intense) and low (cloudy dull or forest) light shows a difference on a scale of amateur vs pro. It really is that stark.
Now, in the UK or in so-so light and better, the 7D is a very, very good camera, especially with prime glass and especially with subjects that are 5 to 200 yards away. In intense, overhead sun, USA or continental European light the 7D is a truly professional level piece of kit (most of the movie "127 Hours" was filmed on a 7D) and you'll wonder why people pay 3 times more to own a 5D, but I'll say this; - if it's a bit cloudy, and you're trying to shoot a Kingfisher 150 yards away then whilst you are boasting about a better zoom level than the next guy on a 5D with the same lens, when you crop the shot to the same size you'll see that his shots are curiously crisper than yours because; firstly, his sensor is simply a better quality piece of silicon than yours, secondly, his sensor is better than yours and thus his camera didn't spend a whole lot of processing time whilst using colour to drive the auto-focus, and thirdly, his sensor is better than yours and thus his shots taken at ISO 2000 are usable keepers whilst yours taken at the same ISO (and less) look like a badly tuned tv screen.
A 7D might save you cash by 'giving the effect' of a 1.6x longer lens but what's the point of getting a crop-factor induced zoom that gives you 9fps of closer, noisier, 'blurrier' pictures? As I said, in bright, sunny conditions the 7D fires on all cylinders and gets to within 90% capability of the 5D but when you're doing long lens stuff in average light I'd go for a 5D MkII as you'll never really use the video.