That's not the point, really. A drive that isn't High Speed capable won't work correctly at 4x on High Speed CD-RW media (when HS CD-RW media first came out there were big warnings on the packs not to use it unless your drive had the High Speed CD-RW logo on it). Similarly High Speed drives that aren't Ultra Speed capable won't work correctly on Ultra Speed CD-RW media.
Your Sony is only specified to work at 4x on CD-RW, so is almost certainly not a High Speed CD-RW drive.
You may struggle to find original CD-RW media now. If this is a problem, a new CD-RW drive shouldn't cost that much. 4x is very slow - modern rewriters are capable of 24x or faster rewriting.