Still 6 speed for manual. Never heard of an 8R80 transmission.
Applying the "standard" .85 drive line loss in reverse puts things at around 490/470 crank. Sick.
The story I got was the 6R80 (6 speed auto) used in the 11-17 cars is being replaced with the 8R80 ( 8 speed auto) in the 2018 car.
I'd use .8 drive line loss for the auto...and .88 for the manual.
The 2015+ auto's came with paddle shifters... which is a hoot to use. Drove a buddy's..... and the kicker is... say if in .. 'manual paddle shifter mode' and in either 2/3/4/5/6th gear..and you come up to a stop sign...when you go to take off, it has enough smarts to start off in 1st gear. Then just up shift through the gears.
The paddle shifter worked slick....shifting up /down. Quick shifts, don't have to take ur right hand off the wheel. Or just stuff into... 'Drive' and drive 'normal'.
Right now, in my 2010, if manually shifted in say 3rd gear...and come to a red light, I'm still in 3rd gear. I can manually shift between 1-2-3 with one finger. Soon as I stuff it into.. Drive.... then it locks into place. Only in drive it has enough smarts to drop into 1st gear at a red light. At least with the TCI ratchet shifter, I had in for a few months, I could manually shift between 1-2-3-D.
I still contend, with that much hp / tq, for DD / HWY use, I wouldn't mess with a blower, maybe LT's + 93/94 tune at most. Heck, Brian was down to 11.49 ET with his NA 14 auto, glass roof, + 5k stall converter + drag slicks, stock suspension. He's on the edge of being booted off the strip.... 'come back with a roll cage'.