With that, how much faster is SSD over disk and then memory over SSD?
DRAM (~100 ns) is very nearly 1000x better latency than SSD (~70 us) which is only 100x faster than disk (~10 ms).
26 microseconds for OCZ Vertex 4 (reads)
No more than 20 microseconds for Corsair Neutron GTX and Vertex 4 (writes):
You should be looking at companies like STEC or higher end Intel SSDs for server applications.