I tried on mine workstation with Vista64 / 16 Gb RAM 8 core Xeon the Retouch Artist speed test with changing the RAID of the scratchdisk.
THere was only 1 second difference in making the scratchdisk Raid 0 or Raid 1 (CS4 16 bits)
In the 16 bits CS4 I saw that efficiency stays almost all the time at 100%. But the 8 bits version of CS4 needs the scratch disk much more.
Making in CS4 16 bits the file much bigger (120Mb) makes also very little difference.
So, can I concluded that CS4 16 bits hardly needs the scratch disk? Investing in more memory is much better then investing in a fast scratch disk?
8 and 16 bits refer to the bit depth used by the image file, while 32 and 64 bits refer to the lenght of the memory words used by the application.
The former should only impact performance in that 16 bits file are larger, while the latter impacts mostly the size of the process that can be handled without using OS or appliation swap.
I am a bit confused which you are refering to here.