I've never shot a .577, however I own and shoot a .500 NE and a .470 NE. IMHO weight, fit, and stock design are very important. Having shot a number of doubles in the above two calibers and similar calibers I have formed a few opinions that I believe in. These comments assume that the fit and design of the stock are optimal for the shooter.
1) a .470 NE should weigh 10-10.75 lbs.
2) a .500 NE should weigh 10.75-11.5 lbs.
3) powder charge type and weight can have a noticeable impact on perceived recoil
4) shooting a large bore bolt or single shot or bolt gun does not give the same "feel" to the recoil as a double.
5) in a gun of proper weight, etc. there is a moderate, all be it noticeable, increase in recoil between the .470 NE and the .500 NE. There is also, however, a noticeable difference in it's effect on large game.

These are my own perceptions and I realize not everyone will agree. But I feel they are worth every penny you paid for them.

Geronimo