I'm thinking of upgrading my 2008 iMac C2D. Searching online for 6770m 6790m gives me nothing that I can make sense of about these GPUs. Anyone have a link with relative performances? I primarily use Aperture (21MP RAW files). Now I know that Aperture heavily uses the GPU, but I wonder just how much difference there is between the GPU models (and memory amounts - 512MB vs. 1GB vs. 2GB) I was thinking of 27" i7 3.4GHz with the 2GB card, but then wondered, "would I be okay with the 21.5" i7 2.8 with the 6770M GPU (with only 512 MB VRAM)". If I bought the 21.5" it would be much easier to afford a nice 27" NEC PA271W monitor (£1000-ish) (2560x1440) -- BUT would the 6770M/512MB GPU really be good for running moderately intensive Aperture work over the two screens (21.5" + 27")? Thanks for any advice/help! Jonathan.