Right but
What you're missing is the point that Apple is rending everything at twice the target/simulated resolution, which IS much bigger than 2560x1440, and THEN for every single frame per second doing a giant quantity of other calculations to generate the compound final resolution ( 2880x1800 ) image. So it's doing a LOT more work for every frame per second than iMacs at 2560x1440. Even a MacBook Air with integrated graphics can drive a 30 inch 2560x1600 monitor relatively smoothly for basic tasks, throw what OS X is trying to do with the retina at it though and you'll see it choke like a 90 year old smoker.
the resolution of the iMac is not so much smaller than the res on the retina. And the iMac deals with this high resolution for SOME time now even at core2duo times. I've never experienced a lag.
Second:
If the many pixels would cause this problem....then....hook up the cinema display with a standard Macbook Pro. This machine is not lagging at all driving even MOOOORE pixels.
Corect me if I'm wrong.
What you're missing is the point that Apple is rending everything at twice the target/simulated resolution, which IS much bigger than 2560x1440, and THEN for every single frame per second doing a giant quantity of other calculations to generate the compound final resolution ( 2880x1800 ) image. So it's doing a LOT more work for every frame per second than iMacs at 2560x1440. Even a MacBook Air with integrated graphics can drive a 30 inch 2560x1600 monitor relatively smoothly for basic tasks, throw what OS X is trying to do with the retina at it though and you'll see it choke like a 90 year old smoker.