The middle of the road 6.4/392 is a great package.
We own a standard 2015 5.7 R/T and while it is a great car, the added power and brakes of the 392 cars would have been a better choice.
It’s funny, I test drove an SP 6M and struggled to find it significantly better. It felt faster on the top end for sure, but around town it just didn’t make me giddy enough to hand over the keys to my R/T. And I didn’t test the brakes enough to form an opinion on those, but I did have the upgraded pads the STP cars came with so..?
At the same time, passing with the 5.7 left me wanting some more RPM and power, definitely the place a 6.4 would shine. Unless maybe the 5.7 had a 6.4 cam. :p