#DHR :
Just pirate the game and try it. Use GeForce experience. For some reason settings everything on high made the game act weird, but using GFE to optimize (which put it almost maxed out) and bumping up some manually made it run at 60 fps @ 1440p.
I've promised myself I won't torrent it. They put soo much work into this game, and I would rather buy it. Yeah, I torrented IV, before I caught it on a steam sale with all the DLC for 8 bucks, but I don't really consider that a REAL gta game. No underwater, no planes, etc.