So.... I'm pretty anxious to get a new tower. My MBP is so much faster than my Dual G5 that I use the laptop for everything nowadays. I've been holding off on a new Mac Pro as the line is nearly 300 days old. We're supposed to get 6 core towers in March. However, I'm fairly annoyed that PS is still running in 32 bit on Mac whereas PC users have been running a 64 bit version for a while now (if they've installed the 64 bit OS).
I've actually been thinking about moving to PC for the tower, so that I can upgrade sooner and have the most flexibility in builds. Not being exposed to Windows at all nowadays, would I be totally frustrated with a PC box? Should I just wait for the new Mac's?
Apart from some filters, Photoshop is still a single core app, so the possibly upcoming 16 core mac won't do much for you.
I made the switch from a G5/2Ghz and a MBP ('08) to a 2008 MacPro 2.8Ghz some time ago, and the MacPro is significantly faster than both, day-and-night
With a decent amount of RAM (12-16GB) and a Raid0 scratch disk (only two drives), it's a very fast system, dealing with Aptus 75 files.
For more info on optimization, look here
I have never used PS (CS4 here) in 64bit Windows, hence I can't comment on possible advantages of the 64bit PhotoShop .
Also, I'm running Windows XP on a seperate harddrive for a few programs - haven't tried Windows 7 yet.
If 7 is any similar to XP in the widest sense, I'll never be tempted to switch from OSX; it's not only the utter ugliness of XP, but also the non-intuitive file and system structure , and vulnerabilty to any hardware, software and malware issues imaginable.
People more capable than me have suggested that Windows needs to be re-done from scratch, much like Apple did with OSX, to become a modern OS.
I'm not very fond of many of Apple's current offerings, in particular the Pro line, but imho you just can't beat the OS for ease of use and mind.