If your servers were doing as much write as reads, then SSDs might not be as fast. I had (raid10) 4 intel 80gb ssd vs (raid10) 4 15k rpm scsi drives, and the scsi drives were faster with heavy innodb writes. You might wanna do some stress benchmarking before going into production if you have heavy writes. Now I'm sure the FusionIO line of drives will probably be faster than SCSI's, though I haven't tested them.