You'll never use a Ferrari for it's intended purpose when you just commute from your apartment to your office. It's a total waste of money.
Instead of spending $3,200+ now, spend $1,500 now, then buy a new computer in three years when it gets slow.
Go waste your money, it'll be old in three years either way.
But you'd have a Ferrari....
one thing I forgot to mention is that I have to have Fusion running as I use a windows based database at work..
so some evenings I might be running Fusion, Safari, mail , Pages, itunes play and a torrent downloading, whilst ripping a dvd...
my MBP really starts to stutter at that point.... Whereas, surely, a Mac Pro would purr ????
(desperate attempt to drum up support).
THIS IS THE VOICE OF REASON SPEAKING:
If you go for a Mac Pro, get the quad. You have a MBP and are having trouble multi-tasking? Well, it has 2 cores, the quad has 4. Thats already 2 times as much multi-tasking. But it doesn't really have 4, it's got 8 virtual, so it can run 8 things completely independently side by side (but still not limited by 4 actual cores). But you are using single threaded programs too, so you will loose out if you buy an octo 2.26 because it is slower than the old 2.66 in that regard. If you buy a quad, you get a 2.66 for cheaper, or you can go for a 2.93 for a similar price and get much much much better single-threaded performance.
From what you have said before, you don't need tons of cores, but everyone can benefit from a couple. The octo would be a bad choice for what I said above and cost you a lot more.
As for RAM being limited to 8GB, who cares. If you are torn between an iMac and a Mac Pro, you obviously don't need more than 8GB because it's the same limit as the iMac.
Now if you buy the Pro, you'll need to buy a screen as well. You can get so so LCDs for $200-$400. Take a look around at Newegg, Futureshop, Best-Buy etc. The iMac's screen is way better than most of the offerings. I am disgusted by the ****** viewing angle of my Samsung syncmaster 2693. But since I usually sit right in front of it, it's not that big a deal. But considering how amazing my old 20inch ACD was... this screen sucks. The only thing I got it for was for multiple input and for that it's great, but you do have much more controls over color ect.
For graphics, it's your choice to get the nvidia or ATI. The ATI is much much faster now... but you may decide to save $200 now, and buy a new card in a year or 2 that is much faster than the current ATI card anyway. The nvidia is still ok, as it is 3 times faster in most tests than the 2600 was.
So my recommendation from what I read (sounds like money is a little tight): 2.66 quad, 3 or 6GB of RAM if you need it, GT120 + a $400 LCD. That will run you $2899 ($2499 without display) vs $2249 for the iMac. Trade off is 2X (or 4) as many cores but with lower clock-speed, upgradable graphics, room for 3 more HDs, PCI cards if you need them (who doesn't want 23 USB ports?), potential (not confirmed) to upgrade CPU in the future and possibly up to 16GB (not confirmed) of RAM.
I didn't say it was the SANE voice of reason did I?