Here are the official SCSI transfer rates for given Mac models according to Apple:
http://support.apple.com/kb/TA29470?viewlocale=en_US
Most of them really suck, of course, since many of them are based on the 53C80, this is no surprise.
Also, for the PB 500 series, when it says "Custom IC" they really mean it's a 85C80 derivative smashed together with the serial controller into one chip, probably to save space/money/etc...
For the PB 500 series, if one can get a Rev C card cage, your system will be far better off booting from a decent CF card than the internal SCSI Bus.
http://support.apple.com/kb/TA29470?viewlocale=en_US
Most of them really suck, of course, since many of them are based on the 53C80, this is no surprise.
Also, for the PB 500 series, when it says "Custom IC" they really mean it's a 85C80 derivative smashed together with the serial controller into one chip, probably to save space/money/etc...
For the PB 500 series, if one can get a Rev C card cage, your system will be far better off booting from a decent CF card than the internal SCSI Bus.