No, nobody can "max" antialiasing. It just keeps going higher and higher the stronger video card you have. A GTX 650 can technically handle 8xMSAA, but you should never use that much because it's a massive performance drop and 4xMSAA looks the same. Stronger video cards can handle 32xMSAA, but that just gets more and more pointless and ridiculous. Past 4x it doesn't even improve quality very noticeably. Generally 4xMSAA is a safe number, but weaker video cards like a 550 or 630 should run 2xMSAA or just no MSAA for optimization.
Your 650 should handle 4xMSAA pretty easily in older games, but you may want to look at 2xMSAA or post/deferred AA in graphically intensive games to save your framerate if you run games at 1080p. Lower resolutions decrease the performance hit of antialiasing, so if you ran at 900p or 720p I'd assume you'd be able to use 4xMSAA whenever it's available.
Sometimes in very old games from 2004 where I'm running at 200+ fps, I enable 8xMSAA just for the tiny increase in quality, but usually that's not a good idea unless you just don't have anything else to use the extra performance on.
Post/deferred antialiasing can be maxed by just about anyone. It's doesn't use "4x" or "2x" or anything. It's usually either on or it's off.
Generally FXAA is lower quality, MLAA is higher quality, and SMAA is highest quality (nearly the same as 4xMSAA), though any of it can be run on almost any video card it's such a low performance drop.
Some FXAA can be pretty good quality as well though, like the stuff used in Borderlands 2 or Metro (it's called AAA in Metro, but really it's custom coded FXAA).
It's worth mentioning that you can turn on FXAA in almost any game with an Nvidia graphics card in your Nvidia Control Panel, but that is not recommended. It's very blurry and ruins detail. Even other FXAA in game menus tends to be higher quality than that.