.....there is always putting the - NoRestrictions - in a txt file in the game folder (command line etc) - which will take out the artificial limit in the game gfx wise (maybe to let the consoles look good) and let you set anything over what your card would "normally" handle, I dont honestly know if this should have helped as much as it has on my rig but it took an unplayable game at medium and let me run it literally flat out except shadows (set to 2 on the slider) - and if you read several other forums on this it will tell you Im not alone in the magical boost it gave me).
Find your gtaiv dir (where gtalauncher is) and create a txt file called
and add your parameters there - write:
and save the file.....simple.
Try it for yourself at the exact same game settings (shut down game - do the txt file - reboot game and reload same save etc) and watch the avg fps go up by about 35% I guesstimate....
Worth a go at the very least as it will let you set over what you could before in the gfx options if it works.