*** warning – speculation mode = ON ***
Caveat: I do not currently drive a 2015 Charger – though I expect that an R/T will be my next car, and I have tested both a 2015 Challenger R/T with the ZF 8-speed automatic and a 2015 Charger R/T.
My ** GUESS ** is that the acceleration will be marginally better, due to more advantageous gearing and quicker shifting. Though it may well be only 2 or 3 tenths to 60, 70, etc. it certainly does feel satisfyingly quick, to me.
Further, my bet is that in identical high speed [ but legal-ish ] driving, the low RPM at cruise for the 8-speed will provide somewhat improved ‘real world’ fuel economy vs. the 2014 [ and before ] 5-speeds – and vs. the EPA numbers. Note that [ see links below ] the EPA added what they termed a High Speed fuel economy test some time ago.
“High Speed: Represents city and highway driving at higher speeds with more aggressive acceleration and braking.” - EPA
However, the average speed here in this added test is still less than 50 MPH, only a very small portion is run at 70 MPH or above, and the several ‘more aggressive’ acceleration portions would largely counter any improvement in the MPG during what I mean when I say ‘high speed’. Meaning: for me, relatively constant 65 to 75 \ 80 MPH cruising in light to moderate traffic. This is where I expect that a meaningful increase in MPG vs. the 5-speed would show up.
Hoping to check that out in the near future . . .