basiclly the shifting mechanism is the same, but the race version comes with a different shaft, the street version uses the oem shaft and knob. the street version is quiet, the race version picks ups vibration and a bit of noise.
I have the street version with the oem shaft and knob.
That is the say to go. quiet , precise shifts.
If you are hesitaiting gettign the GMM , don't. It is the best for the GTO.
One of the first mods you want to do and you will not believe the difference in the shifting. Shift from second to third , shove forward and it goes to the right by itself , shove forward and you got third, it is the cats meow.
race or street is up to you.
if you do put it in , i would also at the time , change out the tranny fluid.
I put in the Royal Purple manual synthetic synchromax fluid. it also made the tranny quieter and smoother. you will need 5 quarts.
tranny takes on M6, 9.3 pints, or close to 4 and a half quarts.
can buy online or check your auto parts store , most good store have it.