8 core Mac for C4d... a few techy Questions

Happy Easter All!
I am just about to order a new Octo-mac ... Primarily for C4d work....

I have a few questions,

1. Which Video Card should I get? (I've checked the Maxon site, & can't
find a list of supported VIdeo cards) I can afford whatever, but I don't
want to waste my money on something that is purely for vanity, I have a
30 Inch Cinema display, I may add a 20 inch also. So the choices are:

NVIDIA GeForce 7300 GT (cheap, possibly underpowered)

ATI Radeon X1900 XT (More expensive, More powerful)

NVIDIA Quadro FX 4500 (REALLY expensive... top of the line)

Which one, if any will support the CG toolkit? (shadows etc...)
Is the Quadro FX worth all the extra cash for a C4d user?

2. How much Ram?.. I currently have 4 gigs, but I want to be future proof.
Is 8 gigs too ridiculous, can C4d, or the OS even use it all?
I am getting the new version of Zbrush soon, I hope it will be able to use
gobs of RAM.

So, 4gigs or 8gigs?

Thank you very much for any advice you guys may have for me
Happy holidays,
Peter Evans