Quote - I have two machines, both running 4Gb, one intel 3GHz and one AMD64 X2 4800+. The AMD64 is running XP64 -- both running 7200 RPM SATA II disks. ... Technicaly, the single core is faster than the dual core, but I have not really seen render times faster for the single core.

I presume your 3 Ghz Intel CPU is based on the older NetBurst architecture, which should indicate that the X2 would yield better results, even though the clock frequency is lower (the AMDs are more efficient). I've not tested AMD64 and Intel (NetBurst) directly against each other in Poser, but I know that the AMD is generally faster clock for clock.

The Core 2 with Intel's new microarchitecture is, however, even more efficient than the AMDs. For example, a 1.86 Ghz Core 2 outperforms an Intel D960 3.6 Ghz (both dualcore) in 3DSMax/Cinema 4D benchmarks (the 3.6 Ghz Intel is about as fast as a 2.2 Ghz AMD X2 4200). So clock-frequency can be very misleading nowadays unless we know what chips we're talking about.

Quote - A single core 64bit system might render slower than a 32bit single core system, all else being equal.

I've performed Poser benchmarks in 64- and 32-bit Windows XP Pro (both on a FX-60 processor), and the results were roughly the same.