I would like to know that as well... I think Vertex will be very good even as single.
Consider APEX - they have higher read speeds - 230MB/x instead 200, same write speed. Don't have cache but I would consider RAID with Apex than Vertex.. hard to say.
One 60GB Vertex will cost £200, one smallest Apex (60GB) will cost about £150.
Another idea is to RAID Solid SSD - 2x30GB will cost you ~£130 - I'm not sure but then you would not have to worry about any speed limits cause RAID will be fast enough...