Good info... I found even more good info in this post
Considering all that I've read in there, I am about to put Royal Purple Max-Gear 75W90 into my car and will be able to test it out within the next day.
Also, if you're using standard, off-the-shelf fluids in your car, you may want to take a look in the thread to see if your fluid is noted as having corrosive properties to the soft materials of your synchros.
Edit (re: Royal Purple): Since I decided to just stay up later and do it... I have to admit, this stuff is VERY nice. The only thing that was said about it was that the gears were louder, though I can barely tell. Mine whine a lot as it is, and my car makes a lot of strange noises, but I can't hear anything over normal when driving, just my standard 1st gear decel noise. Shifting has to take 40-50% less force to get the shifter to select the gear. Overall I'm very impressed.