OH MY GOD.
Made the switch to the AMSOIL Severe Gear 75w-110 gearbox and diff oil today. Holy Crap! Nice smooth shifting, about half the gear noise (even my passengers commented, "what did you do to this thing?"), and should take the abuse. This is coming from a fairly short run of Motul Gear 300 full synthetic, that was changed between the Pro Finale and Solo Nationals last year (so about 10 autocrosses and one ProSolo, all with multiple drivers...no real "winter" downtime here.... and about 10K street miles). By comparison, the Motul would be notchy when "cold", start feeling okay but noisy, get really noisy when hot, and then finally get more notchy. Screw that. The oil that came out was dark but not stinky, and there was only the standard grey paste on the drain bolt magnet, no shards...so I guess the Motul was doing its job, but loud as heck and no fun to shift.
Anyway, +a million on the Severe Gear, whatever weight you choose.