Upload & Sell: On
I have worked to build up a better wildlife kit over the last several years. I presently have a 7D, 200f2.8, ef1.4x, 300f4is, & 500f4. Lenses like the 500f4 have their use along side something more compact like the 300f4. I don't see a compelling reason to get the 300f2.8 over the 300f4 unless you want to use a 2x teleconverter. The portability of the 300f4 is an important attribute.
I generally do my wildlife shooting with my longest lens on the 7d, but have used the 5d2 from time to time. A great "non-photo" vacation/travel setup for me (if wildlife shooting is a possibility) is a 35-70 zoom, 1.4x, 300f4 & 5d2.