i7 vs Dual-quad core xeon's(8 cores)

I will be in the market for a new mac after wow starts to require intel based cpu's and my question is this: Is a 27.5" iMac with a core i7 better than a used mac pro dual quad core 2.8ghz? I can get them relatively about the same price (imac new, mac pro used.) The mac pro will be about the same as the imac once i upgrade the video card. But as far as performance wise, which is better? I will be running osx, windows, and linux (hopefully all 3 at the same time) and doing alittle video editing and much software development and graphics work from with in all three OS's. Just to confirm, i can have a second monitor on the imac correct?

This was posted in respons to a question of mine in another thread. It might help as it it includes the i7. You need to know what specific CPU is in the MacPro:

Cinebench and Geekbench results for 2010 Mac Pros

It would be the 2008 xeon 5400's, i think the harper cpu's. Which are getting a run for its money by the i7. Which would mean its almost better to buy the i7 imac than the used mac pro. But, question is how well is the graphics on the imac? Do they perform well? or are they a bottleneck for the i7 in games? Is it possible to connect 1 or 2 monitors up to the imac?