actually, you would want to try and share the DLLs, thereby reducing the number of duplicate DLLs in memory. the reason you get better performance across multi drives is due to the game loading non-DLL files, and spreading the reads across multiple readers. (drive reads and writes are sequential)

theoretically, if you could put the DLLs into a common directory and put that directory in the path, then they should share the DLLs. then you put the data files across multi drives.. that'd probably be the best performance, without getting into stripping w/ RAID.