I got the XPS 15 with the second generation i7 2670QM and it kicks butt. I have thrown Adobe CS6 Photoshop, After Effects, Premiere Pro, and Illistrator at it and it blows right past it. I didn't opt for the NVIDIA 540M GT upgrade because it was too much money, but the 525M still kicks through pretty much every game I have thrown at it-though some settings need to be lowered to get 40+ FPS that I prefer. The HD screen is also the best there is in a laptop.
There is almost no speed difference in from the 2nd to the 3rd generation Intel i-series chips; about 5-8%. You also get a more power efficient chip and the integrated graphics chip is waaaayyyy better, but at the price range your looking at it wouldn't matter as it would come with a discrete chip.
Anyways, I recommend the XPS series
. The new generation's design is much better, in my opinion anyways.
Windows 7 Home Premium
Intel i7 2670QM
8GB DDR3 1333 RAM
NVIDIA 525M GT
750GB 7200RPM HDD