If I don't want to be swapping out rear diffs every other race, yes.
with the stock 4.1 rear diff, I MUST run an overdrive for 2 of the local tracks since I'm shifting into 5th halfway down the front straight.
for the shorter tracks, I use gears 2,3,4 on the stock tranny; on the longer tracks, I use 3,4,5.

I guess I could always hunt down a 3.6 or maybe 3.9 rear end so I wouldn't need the overdrive, but then I would suffer astronomically on the shorter tracks if I didn't swap the diff with my 4.1 or 4.6 between tracks. I'd rather spend a bit more money and get a 5 spd tranny with an overdrive on it and not have to constantly swap parts around.

I'm considering G force's 5 spd synchro box with road race ratios, but would rather go with a dog box. Any experience with how well the synchro boxes work and last?