Cycles rendering time differs significantly on machines with nearly identical specs.

Hello,

Just came across with a problem with significant rendering time differences between two MacPros. Using Cycles.

The first one:
2x2.8GHz Quad-Core Intel Xeon
10GB 667 MHz DDR2 DIMM
ATI Radeon HD2600XT

The second one:
2x3GHz Quad-Core Intel Xeon
8GB 667 MHz DDR2 DIMM
ATI Radeon X1900

Both running OS X Snow leopard.

Rendering with identical file, the fist one (2x2.8GHz) rendered 11 times faster than the second one (2x3GHz).
Tested the scene out with f93bc76 and 517094a. Same result. On both cases, all 8 cores are being used fully. Plenty of memory free.

Is there any known issues that would explain this behavior? Or might this be just a case of malfunctioning hardware?

-Jaalto