Athlon 64 (K8) does have a couple of big advantages over the K7 chips; the integrated memory controller and SSE2 support are pretty important improvements, not even counting the 64 bit support. My desktop system is an Athlon XP 1800 (Nforce2 MB) w/ 1 Gig of RAM and my laptop is an Athlon 64 3200 w/ 1 Gig of RAM. In side by side renders, the XP will take on average 3x longer than the 64. Since you already have a pretty high end XP, I don't know if the improvement would be that dramatic, and I don't know how much of a boost OpenGL really gives Poser (the desktop has a 64mb GeForce4, the laptop has a 128MB Radeon 9700), but the Athlon 64 should still give you a big performance boost just owing to the better architecture. In every benchmark I've ever seen, the lowest end Athlon 64 destroys the highest end Athlon XP (and the Pentium 4).