Need advice on new desktop (Mac)

Hi all!

I'm new to this forum.

I'm a professional photographer and I'm thinking of trying out Corel's Painter X.

Firstly, my current setup:-

MacBook Pro 17" Glossy (4GB RAM), EiZo CG241W LCD Monitor, Wacom Intous3, LaCie 250GB Firewire 800 external 'scratch' hard drive. Software I often use are Adobe Photoshop CS3 & Lightroom, Nikon Capture NX, Canon DPP, PhotoKit Sharpener and Genuine Fractals. Printers are Epson 3800(K3) and 4800(Piezography K7). Monitor calibration is X-rite.

I'll be getting a new desktop before the end of the year, probably just after Apple releases 'Leopard'. I'm currently looking at the Mac Pro. What specs would you guys recommend for someone who'll be using Lightroom, Photoshop CS3 and Painter X simultaneously. I will be working on large files. My file sizes in Photoshop usually go above 500mb and sometimes more than 1gb. This is before the image is flattened and interpolation is applied.

I expect to use this new setup for at least 3-4 years, with maybe a RAM upgrade in between.

- Is the quadcore CPU option overkill?

- 4 or 8 gigs RAM?

- Graphics card? does Painter X take advantage of a fast card? If yes, is the 512mb ATI option sufficient?

- RAID. Yes or No?

Thanx in advance.