and yes I have considered this in detail I really really want to go to Redline MT fluid, but since I had the tranny fail, I am hesitant.

I have missed second a few times due to the notchy shift going into second at high rpms

I am glad that the Subaru warranties call for GL-5 approved gear oil. Typically fluids by NEO, Redline and Amsoil meet or exceed what the manufacturer specifies. Voiding your warranty just for changing your transmission fluid/gear oil ranks right up there with voiding a warranty for replacing the sparkplugs on your car.

I would think this would be more of an issue for people with automatic transmissions. Since, when you drain transmisison fluid, you really dont get all of it out. Typically it has to be flushed out. What would be interesting is to explore what a combination of fluids would do to the internals of your transmission.