Idiots guide to graphics cards

[CommanderJameson]

While my iMac was being a prima donna, I did a spot of idle computer-shopping.

Now, I've been out of the PC components loop for about six years (unless you're talking about HDLC cards and other tedious stuff) and I've completely lost track of what's what in graphics.

The iMac I've got has an NVidia 7600GT. The iMac I'm idly pondering (21 inch, 3GHz C2D, 4GB RAM, fact fans) has an ATI Radeon 4670.

I'm assuming that the latter's a bit quicker than the former, simply based on the three and a bit years there are between the two.

Is it much quicker? Will I be able to, for example, run Left 4 Dead 2 with everything turned up to max at the native resolution (1920x1040)?

While I'm here, is the Intel i5 CPU dramatically faster than a 3GHz Core 2 Duo, or would spending the extra on the 27-inch iMac just be digital willy-waving?

[LukeBird]

Not sure on the C2D vs. i5 argument, it certainly will be quicker, but whether it would be enough to make a difference day-to-day I'm not so sure.
The graphics card will be very different. It will definitely be capable of running Left 4 Dead 2 at native resolution with most of the eye candy on, probably not all of it, but certainly enough to be very impressive!