POV-Ray rendering
POV-Ray just recently made the move to 64-bit binaries, and thanks to the nifty SMPOV distributed rendering utility, we've been able to make it multithreaded, as well. SMPOV spins off any number of instances of the POV-Ray renderer, and it will bisect the scene in several different ways. For this scene, the best choice was to divide the screen up horizontally between the different threads, which provides a fairly even workload.

With four threads taking full advantage of Hyper-Threading it's fairly close, but the Athlon 64 X2 4800+ turns in a faster render time than the Pentium XE 840. Similarly, the X2 4200+ beats out the Pentium D 840 here.