The available write speeds really depend on the firmware in your drive.
The firmware within the drive has a list of supported media and what speeds those media can be burned at.
Your CD-R media may or may not be supported at higher than rated speed - or in some cases it might only be supported at lower speeds.
Some burning programs may not be able to provide you with a choice of burning speeds, but no burning program will be able to force a drive to burn CD at a speed that isn't supported by the drive.
As TimC wrote, you will not be able to burn CD-RW media at higher than rated speed, because that would probably destroy the disc.
Only CD-R media (and DVD+/-R media) can sometimes be burned at higher than rated speed.