I have used the old Raptor 150's times 4 in a raid 0 array for years. I thought that they were the best ever. And they were. Until SSD's showed up and gamers started loading into newer games before me.
I ran some drive speed checking, benchmarks and found that my vaunted Raid 0 Raptors have indeed passed by.
It's interesting you note that you don't use much space. I have seen the same myself.
Thus you may take advantage of that by trying a small number of SSD's with small capacity in RAID totalling a few hundred gigabytes. You may be able then to outperform more expensive Raids.
I actually have 4 60gb that I plan to test and then sell.
they are the vertex plus ones that are the cheapest on the market at that size.
I have some other stuff on them now i need to move then will give it a try.