NAT Server Performance, SMP box or Single CPU box?

[Donato Diaz]

Hello,
I have read in different lists that some people are having problem doing 
NAT with SMP Servers, due to the way the kernel manage conntrack with 
both CPUs.
NAT runs slower on Server SMP with two CPUs?
Is it better a Server with one faster CPU than a server with two CPUs?
I need to buy a NAT Server for +1500 users. I would like to know if an 
SMP Server with two CPUs is the best choice.

Any help would be really appreciated.
Thanks all,
Donato.