Should you do decide to go to iMac instead of Mac Pro, do yourself the favour and bring your video camera / equipement to the mac store and test it out against the iMac model you plan to purchase. I discovered the hard way that none of my video cameras would work with ANY of the Aluminum framed Intel based iMacs what so ever, but they all would work 100% with any and every other Mac computer in the store.
This is why I bought the Mac Pro after returning the iMac. I have the new old one, it's decently fast enough though slower than my PC quad core when doing video work.
There's no doubt the iMac concept is nifty, an all in one package but has little expandability.. If you camcorders work with the iMac and you're not a power user, and only plan to do the occassional video editing work, an iMac would be a nice system.. but heed what many say.. once you get hooked, you'll be wishing you had more.. As the old saying goes: "Go big or Stay Home"
If I had to do it all over again, knowing NOW what I know after such difficulties, I would have gone for the 8 core system. I don't game on the MacPro, kinda not the right system for it in my opinion, but its nice for photo and video editing and this is where the 8 cores will kick in the most. For general every day use, you'd most likely not see the speed but when you're crunching huge numbers like in AV work, you'll fer sur see it.
Right now, I'm mulling over either selling this quad Mac Pro and going for the 8 core.. or upgrading this old/new Mac Pro with an 8 core (2 quads). Mine currently has the two duo cores 2.66 in it. No idea on how to go about this but research should hopefully get me there..
Best of luck.. cheers