I've been messing with oils for a long time, and sending off for oil analysis to actually know what is happening in there. Just not saying I like something because it feels "good".
So I had about 130k of testing between Toyota WS and Amsoil low viscosity Signature series ATF in a different Toyota transmission. After running back a forth in 40k runs, without getting too into the numbers, they are both really good oils, Amsoil is just slightly better on a couple of aspects that could make it run a bit cooler. I went with Amsoil because of that and the fact that I can get it much cheaper than Toyota WS.
But I'll be honest after the first change I did at 40k, every change after that the fluid was above 85% of its life. Really once the transmission is broken in (no highway driving and only easy grandma like driving on the first 500 miles) those transmission could just run and run on the second fill.