The XPS 435 (Studio) is a new PC offered by Dell, it comes with a core i7 920 and it DOES have PCI-E 2.0. The only issue here is that it comes with a 475/550w PSU depending on the model.
My suggestion is that you go with a GTX 260 (216) and you will be fine. If you want to install a GTX 295 you will need to upgrade the PSU.
@ obsidian, my dell XPS 400 is almost 4 years old and it has a GTS 250 (DUAL SLOT) just FYI.....
hehe, don't bet your ass, lol you might lose and then what will you do???