Would still welcome any feedback regarding the extent to which formatting your drive with a larger cluster size effects CS2 performance.
Adobe this is one item that is missing from the very good FAQ on how to, "Optimize performance of Photoshop (CS2 on Windows)". This might be worth including if it can make a difference, including any pros and cons that need to be considered.
Regarding one reason you may not want to exceed the maximum default settings, 4,096 bytes (4 KB), is that "NTFS file compression is not possible on drives with a larger allocation size." according to Microsoft.
Microsoft - "The Default Cluster Size for the NTFS and FAT File Systems"
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http://support.microsoft.com/kb/314878>
I never use NTFS compression on my image files, so I am not concerned about that, but it may matter to some of you. Here is information on NTFS compression...
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http://support.microsoft.com/kb/307987>