Just looking at a 2nd hand iMac 27" screen 2.8Ghz i7 CPU 8GB Memory ATI Radeon HD 4850 with 512mb Not sure when bought but has about a year and a half warranty still on it. Specs seem good, although I'm concerned about how good, or rather how poor the 4850 graphics chip/card is? To me, looking at the other specs, it feels like it's very much the weak link in the chain. The latest iMacs have much much faster graphics don't they? Thoughts?