Here's a 3ds max render comparison at least:
http://techreport.com/reviews/2005q2/athlon64-x2/index.x?pg=8
Dual Opteron 275: 1min. 10 sec.
Dual Xeon 3.4GHz: 2 min. 7 sec.
The Opteron pulls ahead because it is Dual Core and 3ds max is properly multi-threaded as you can see from the utilization charts for each CPU core.
The Select pulldown box further down on this page also has other benchmarks.