I have a CF-39 and a first-generation 27" imac. The 3.06 c2d, with 8GB of RAM and the 512mb video card. It works fine. It's not blazing-fast, but it handles the files perfectly adequately and I don't find I spend much time drumming my fingers, waiting for the files to process. If you ask it to process 800 files it's going to take a while, but given what it is I cannot, for one second, fault the imac from a speed point of view.
Things to consider, though: More RAM is better - I went from 4GB to 8GB and the difference was remarkable; you only get one hard drive and one FW 800 port, which is challenging if you're shooting tethered and you want to have a backup running. I use a powered firewire hub from unibrain, and it works really well.
Personally, I would never buy a Mac Pro again. I had an old G5 which worked great for years but if I want a faster computer I'll just buy a faster imac. The computer, delivered to my door, all in, was less than $2000. The additional ram was a bit more, but that's a loooong way from a basic Mac Pro and an NEC or an Eizo monitor. Or an Apple monitor. One moment... Just checked pricing online. Today only (Black Friday) The basic imac with 8GB of RAM is $1918 Canadian, shipped to your door. A basic Mac Pro with 8GB of RAM and a 27" monitor is $4100, shipped to your door.
It's the best bang for your buck out there.
Oh, and I also have a 3-year-old 15" MBP. Running Phocus on it is a triumph of hope over experience...