400mm f/5.6L on full frame
I currently have a 7D, 5D2 and 5D3. I agree with your impression from your friends 60D. Basically the pixel quality of the 7D is not good enough when compared to the phenomenal pixel quality in both the 5D2 and 5D3 (which are fairly even). Therefore, I've tried to use the 7D for more reach since purchasing the 5D3 but in the end I've always been more impressed by a crop of the 5D3 vs a native 7D. I've been using the 100-400 lens and in these cases at 400mm f/5.6 pretty much all the time.
I also have the 1.4TCIII and have tried that on the 100-400 with taped pins to allow the camera to try and AF. With the 5D3 it works okay but not good enough for BIF, it is fine for a static bird/animal but sometimes hunts a bit.
I haven't tried the 1.4 TC with the 5D2 but would assume it wouldn't perform very well. Maybe the centre point would be okay???
Basically getting a crop camera or getting the TC are both not great options and you probably won't be satisfied with either solution. Unfortunately, the only way to get what you want is to get a longer lens or a wider aperture 400mm lens. The options of course would be 500 or 600 f/4 mk1 or II; 400f/4DO with TC, 400 f/2.8 with TC (1.4 or 2.0), 800L!!
Personally, I'm in the same sort of situation and I've tried the two cheaper options....I have already ordered the 600II and I am patiently waiting for one to arrive at my dealer. So that shows where my "research" has landed me!!