i'll say this, on 40s, my truck "feels" right when I dump 100 Octane in it.
When I go back to 93, it feels like an absolute slug comparatively. when I run 91, I'm constantly banging it off the limiter and calling the truck every dirty word that I can muster.
I know a lot of folks want to believe in the ecoboost, but man..... there truly is no replacement for displacement.
When RMB punches the motor out to a 4.2, along with turbos to match, it puts it down, even on pump gas.
The big challenge is, If you're going to dump $50K-ish into building out the motor and supporting mods to put down big power, you could have dropped 30-35K into a supercharged coyote, had a V8 soundtrack, with a way snappier driving feel down low and an arguably more reliable motor with commonly available replacement parts. The tunes that TMX worked out with Petty's Garage make those trucks REALLLLLLY fun to drive.
I wonder if going to deeper gears might help get you in a powerband that is more appropriate. I also wonder if maybe upgrading the transmission with the suncoast kit (clutches and a billet TC) will help you put more of the power down.
I'm moving to 5.14s in hopes that I get a little bit better performance out of my truck. The math says that's even with 5.14s, my top speed will be 203mph on 40s.
, so I wouldn't worry about decreasing your top speed by going to deeper gears.