Be sure to see my new site MacPerformanceGuide.com.
Courtesy (loan) of Other World Computing (see All About Mac Pro Memory), I have 32GB of memory and four of the new 1.5GB Seagate drives coming. These items will be put to the test and my DAP article Optimizing Photoshop Performance guide updated accordingly.
A Mac Pro memory riser card with 4 FB-DIMMS
The short story on Photoshop performance for large files: striped RAID and 16GB memory. See All About Mac Pro Memory.