I think, that SH-S means something special.
SH-S223 and SH-S203 (same: TS-H653B) reach higher speeds on some disc models.
DVD-R and +R are reached to up to ×22 by the SH-S models, and ×24 by SH-224.
But dual layer discs: instead of ×8: -R DL × and +R DL ×16.
DVD-RAM: Only ×5 by SH-224 (and also HL-DT-ST drives), but ×12 by SH-S.
CD-RW by SH-S up to ×32 (UltraSpeedPlus+), but only ×24 by the other one.
I know, that burning at lower speeds offers higher quality, but that's no reason to limit the speeds. Speed is useful for mass distribution. A readable quality is still reached at maximum speed.