I have used Golden Spectro, Maxima, Mobil, .... in the transmission and it worked OK but like all the other heavier weight lubes I tried it caused the clutch to drag especially when cold. I finally decided to try Type F ATF and that was what I stuck with until I tried Powershift ATF (used in bulldozers, etc...) which is basically the same thing just a little heavier and better at dealing with the wear particles from the clutch material. The Type F was great though and would suggest it to anybody with a 2 stroke that doesn't want to by a 5 gallon pail of Powershift fluid.
As far a premix oil. Any of the top shelf synthetics work well. I used Silkolene, Maxima, Bel-Ray, and Motul. I was really liking the Motul at 50:1 but the price was a bit steep so I tried Amsoil Series 2000 at 50:1 and have no looked back. It is the cleanest burning premix oil I have found (Motul is VERY close). My piston, power valve and head have no buildup to speak of and show no wear. I run it in both my 360 and son's SX50 with zero problems.