iMac Speed

I have the same Mac Pro that you have, and also have a 2 year old iMac i7.  There is no contest.  The iMac smokes it on everything except internal storage.

If I were you, I would get an iMac with a SSD, and attach disks USB3 to it for storage.  Get 8 gigs of Ram and you are set!  I also have a Drobo, and that might be a good fit for you now that they have a Thunderbolt version.  Get the iMac when it comes out!!!

Kevin