Amazing but true: how you configure and use Photoshop CS5 can make an enormous difference in performance. It can be 5X slower than CS4, or 3X faster. Wow!
But there is also a “warm up” issue with memory allocation that can mean a 6X variation in performance with CS5 that can make it 2-4X slower than CS4 (depending on the size of the job).
The good news is that once “warmed up”, the 64-bit CS5 is 3.3X faster on the diglloydHuge benchmark (with 64GB memory installed on 8-core Mac Pro).
See my revealing Optimizing Photoshop CS5 report.