Best hardware platform

Well I ported my old client list to the new system and played around with it a bit and I think it’s going to work.

I am gettign ready to purchase the main computer fro my clinic.

I need to know one thing for this:

Core 2 duo, quad, Core i7, or xeon? If YOU had to pick the best possible situation, which would you gof or? I am looking for maximum performance in the database. Drives will be velociraptors for the C2D or i7 setups, likely SAS if I go xeon.
Total network will be three computers initially (other two will be laptops C2D 2.5ghz range) but expanding to five in the coming years.

so the big question is – will i need 4 cores for this app (the server will be dedicated) or will a C2D be just as fast as the quad cores??

FYI, current imported client list is just under 1000 people already, if this matters.

Thanks for the help!