1) Let's wait for the benchmarks
2) Yes, the gap has narrowed (my decision earlier this year would have been more difficult if these iMacs had been out).
3) Now that I made the iMac to MacPro jump, I REALLY like being able to swap out HD and graphics cards.
Performance as far as processor and memory are concerned, on most real world stuff, should be similar and there shouldn't be grounds for deciding between them in this area.
The Mac Pro uses a "higher end" chipset and you get the expansion options, access to more powerful graphics cards, more internal drives and other features one might desire for more demanding computing.
The iMac gives you access to the power and a display for a lower price.