The graphic card would have very little to do with this to be honest. The processor would handle the 'flat' image on your screen outputted via the graphics card. Graphic cards mainly handle 3d grahics, say, in games, video processing and increasingly other processes offloaded from the CPU. The slowness in getting the image on your screen is most likely down to slow disks, processor or lack of RAM. I'd look there first when it comes to upgrades.