Toribash
dynamic and persistent online world for 16 players
by IGN

Imo 16 players in gta is enough to be ubber messy but fun.
But that's the standard for consoles, Mount & blade warband originally capsed for 64 players raised its limit (because of modders) to 200 players. It was possible to go further but most players' pc couldn't handle it.

GTA V mp will be fuckin epicness