Most chipsets seem to be able to do no more bandwidth than a single Vertex at the maximum sequential speed. The X58 chipset seems to be able to do 3 (there may be a little bit capped). All hardware controllers I'm aware of come with cache, although since the drives are cached this won't give a massive performance increase. The Dell 5/i might do for 2. An Adaptec 2405 or equivalent would do 3. A 5 series Adaptec would do 4. Adaptec aren't the only manufacturers out there.