I think 30mb/sec was quite hard to get with CSPPC - my figures were between 22 - 26 IIRC. diid see some a bit higher but 30 can't remember. Well, somebody wrote here 2005:
CSMKIII and CSPPC offer theoretical maximum of 40MB/s transfer, for UW-SCSI. With a really good drive, I've managed to go slightly above 30MB/s.