The only significant un-upgradable difference between the two MacBook Pros seems to be the amount of RAM in the video card. Does 256mb vs. 512mb make a real difference? For gaming, photoshop, video editing, video playback, etc. I'm interested in one of the new Macbook Pros but $500 seems like a lot for a little more video RAM. Also, is the amount of ram in the video card upgradable?