Since Tigers' Core Imaging is going to require 64 MB minimum, I'd personally go with the 128 MB. Your gonna want all the VRAM you can get, plus then, dont forget, you CANT upgrade the VRAM. So you might as well drop the extra 100 and get the extra VRAM. Plus, 128MB of VRAM will make Quartz Extreme and Expose run smoothly on a 20" or higher monitor.