I have both rifles and have used them both in Tanzania on buffalo. Both work superbly as they are both classic elephant stoppers and therefore, why should'nt they work on buffalo, provided you do your part. My .577 weighs in at 13.5 pounds and the .600 at 15.5 pounds and in fact, I find the recoil of the .600 to be less(regulated at the 100gr cordite load)however, IMO both are extremely tolerable. I have shot 9 buffalo with the .577 and 12 with the .600 and can say that both are sledgehammers in every way, especially if you hit bone. I have not had to face a charge with either, but I am confident that with either one of these rifles in hand, things should go well provided I aim relatively straight. The point is I like both rifles and I think that they are both just as good but I think that I would lean slightly towards the .600 simply because the rifle that I have fits me so well and is very accurate(I have lungshot an impala with it at 150 yards) I also like the blunt shape of the bullet. The shells are a little expensive, but the heads are the same price as the .577.
With regards to lugging a heavy rifle about all day, I feel that, just like any exercise, you merely need to practice and it gets easier. After all, four pounds extra weight, to me is not much at all.

wadeb