Yeah that wouldn’t make much sense, the OSSC is just basically a line doubler and the sound would basically be passthrough. The OSSC can’t actually alter the speed that the Mega Drive itself runs at.
As for the PAL vs NTSC thing, I think us PAL users got it bad for a long time. Even the PS2 only allows you to choose 60Hz in certain titles while most are limited to 50Hz. A lot of the games were 30fps, so the PAL versions are actually only 25fps. Believe me, that 5fps makes a huge difference if you compare them. The one good thing is that aside from the lower fps on those PAL titles, the PAL games on PS2 are actually speed optimised instead of going slower like the older systems did.