I've had 1.6 60' on 235/60s BFGs dr on my car when it was nearly stock. I've cut 1.5s on 255 MT dr when in the mid to lowI 11s. I've cut 1.5s with 275 MT dr at 11 flat. It was around 112 mph at the traps that I went to the taller tire. Went from 12 flat to 11.7 with no change than the tires. Much has to do with your rpm at the traps. A taller tire may put your rpm too low for best power or in a better area if you have mods that raise the power band. Just my observations.