Ah yes, you have to turn cheats on in the mame.ini to see the CPU slider.
(under CORE MISC OPTIONS)
cheat 1
The slider doesn't show % decimals so it can be difficult to adjust with precision, hence also quoting the slider value recorded in the game's config file (garou.cfg find it in the cfg folder)
There probably aren't many games needing super precise OC, but it's a good thing to know.
I think the neogeo driver must be among the most correct now, at least code-wise, but since MAME lacks wait states emulation even the best drivers will run games inaccurately, even with a proper 15khz setup.
To get 'grail' like things like wait states emulation or beam racing I think they'd need to rewrite almost everything, huge part of the emulator, drivers, even redump games.
So you know...MAME redone almost from scratch...will never happen. Or we'll be so old we won't care anymore (prolly already the vast majority of ppl don't care/know about accuracy, and the arcades nostalgia is seriously fading with the growing numbers of new emu users who didn't grow up thru the same era)
Anyway, we can hack like this, guess it's better than nothing eh. ^^