To be honest, i went 8-8-4-4 buttons for players 1-2-3-4, and to be frank, i feel it's the best amount of buttons. I've come across tons of 4 player games that use 3 buttons (gauntlets, sports games), but i've never come across anything that i feel i'm missing buttons for. I emulate everything up to N64 (MarioKart64 and Super Smash Brothers) and dreamcast (gauntlet legends), and i just haven't come across any games that need more than 4 buttons for p3 and p4.