The CD-RW high speed is rated for ×8-×12, so drives mostly only offer ×10.
But several old drives such as the SH-S182 offer to write at ×10 or ×4. This can be very interesting.
I can not test, whether ×4 works, because that S182 was from a dumped school computer, and does only write CD-R. Even if I write CD-RW×10 at ×10, it does just effectively blank the disc.
What purpose did writing a CD-RW×10 at ×4 speed preserve?