Way Steam is implemented allows for usage of libraries provided by Valve, which means that if drivers and hardware are capable of running game, then game from Steam should work.
If games wouldn't work, it would mean that some part is broken/insufficient (drivers, hardware) and needs repair/replacement.
To put it in simple way: except hardware and proprietary drivers you shouldn't have to worry whether game will work. (Just make sure that there is Linux version of it.)
Oh, and don't install 32 bit version of Sabayon, your hardware, since you're planning to play games, should be capable of running 64 bit version. It doesn't affect Steam and games on it, since Steam runs on it's own libraries (speaking from experience).