Just a quick update since I started this thread back in '16. I've been using ATF in my primary for 20k now and my initial impressions haven't changed, I really like the clutch feel and wear seems to be excellent judging from the looks of the drain plug and the old fluid (unscientific I know). My most recent run was 7,500 miles and the plug had a about a bb's size accumulation of metallic paste on the magnet, no shards or anything that would indicate aggressive wear. The fluid was still a burgundy color, not black by any means, I have no doubt there was plenty of life left in it, from here on it'll be 10k OCI's. Clutch performance was as good at 7,500 ad it was on mile 1. And those miles included some serious stop and go uphill in the Phoenix heat.
I'm sticking with Mobil 1 Syn ATF, but honestly I can't tell a difference in feel from regular old Valvoline Dex/Merc ATF. I'm using the Mobil 1 just because I figure I synthetic will withstand the heat better here in Phoenix over the long OCI's.
Mobil 1 Syn ATF + Redline Heavy Shockproof = clutch and shifting wonderland, even in my older RK w/ 40k on it.