I am interested in upgrading laptop and would like to play a few games. However, many Mac games require 528vram. But, one of the lower end MacBook Pros has an Intel 3000, with about 300mb of vram, and an AMD Radeon with 256mb of vram. My question is, will the graphics cards work independently, only giving me 348mb of vram or 256mb of vram. Or will they work together giving me more vram?