DVD DL and DVD+ rotate slightly faster at same speed setting

[TL7]

Let's assume the speed setting ×8.

If I set all different DVD types to ×8 CAV, the rotation speed does slightly vary.

DVD-ROM,-R,-RW rotate at an equal speed at the same speed setting (example: ×8).
DVD-ROM DL,-R DL, +R and +RW rotate slightly faster at same ×8 speed setting.
DVD+R DL (probably +RW DL too, if released) does rotate even faster at same ×8 speed setting.

It appears that DVD+R DL ×8 CAV equals the same rotation speed as DVD-ROM would at approximately ×9 CAV.
Is that deliberately? What is the cause?

×9 is no standard speed. The LG GH24 series also read DVD-RW and +RW at ×13, not ×12.

[Ian]

Could be a slight difference in the pits and lands. If they're slightly larger, it would require a faster rotation speed to hit 8x (~10,500 KB/s).

Do you have any screenshots showing examples? Kinda curious myself now.