I used mainframes, too, but that isn't what I use now. I use what I like, not what I was forced to use.
Because paging is always going to be slower than RAM, I am surprised that 512 is enough, or that you think you need to RAID the 36s. Comparing Raptors maybe? I think, having used the original and some current 10K and 15K drives, that you might find using a single drive, or outer tracks probably, to be as good or better than the RAID setup you used or plan to implement. Most, I would try a non-RAID for awhile. I keep going back and forth, and right now found that four non-RAID drives (all same size) is 'smoother' and faster and better optimized - for me.
yes, different operating systems have different characteristics, but tracks, sectors and cylinders don't change. I use to have to code databases to use certain sectors and cylinders, that and tweak the OS performance over our "DASD farm."