Let's do this based on scores of 3dmark05:
x1400 - 1600
Nvidia 6600 - 2400
ATi X1600 - 4100
Say the X1600 gets underclocked about 20%, which is typical by most companies. Then assuming we maintain our clock:speed ratio..you'd get about 3300 points in 3Dmark.... So yes, it would still be much better than the 6600.. But the thing is, if the video card is underclocked, you can easily clock it back to the regular clock when you want to play games, as well as have your laptop run nice and cool when you're just doing word processing..
I actually would prefer laptops that have underclocked video performance in 2D mode ... They run much cooler
