Hyperspeed is right: for booting CDs you'd probably have an RDB layout on the CD. With proper CDFS installed in RDB it might even work to boot an ISO/Rockridge CDROM, probably depending on ROM version, compatibility of CDFS, luck, etc. Dunno if there are tools around to build such a disk though. For spinup timeout you'll have to look at your SCSI HBA options - e.g. the A3k internal one can be set to boot from slow spinup drives.
Whether Execute is internal or not does not matter one bit since the OS manages booting from HDs and FDs just fine... ('Execute' is just a stub calling an OS function that's resides in ROM, so any code is free to call that by itself.)
