I use "redline shockproof lightweight" in my r33 box.
it's a synthetic oil that gives you all the nice cold shift action without waiting for the oil to heat up - and i found it made a big difference in being able to smash it from gear to gear, without waiting for the synchros to catch up. It's also put up with an awful lot of abuse and no component failures yet. (I don't know if this is because of the oil or the box design
)
I do know that on the redline website it says that it's "not recommended" for synchro boxes, but a lot of the skyline guys seem to run it without a hitch. - I think you can get a 'superlight' incarnation of it that is 'safe' to use on synchro'd gearboxes.
my mate runs the superlight in his 350z box and it no longer sticks when cold.
as far as lubrication goes, and shock loads on gears etc - I know a lot of the drift guys run and swear by the lighweight shockproof (aka smurfs blood) in their cars, which see a LOT of gearbox abuse in the form of clutch dumps etc.
