My plan with splitting tempdb across three different storage systems was because I didn't have any fast storage to isolate the files on their own. My understanding is that SQL would use the tempdb files in round robin, and while I assume you're correct that some tempdb files would perform faster than others, several concurrent processes would be able to access tempdb data using the three storage systems simultaneously. Since tempdb would be in contention with other I/O on each storage system.

I think with the RAMDisk solution, it would probably be best to put all of the tempdb files on the RAMDisk together - instead of split with the SSD like I originally posted. What are your thoughts, am I misunderstanding something?