Gains are had for sure with no catalyst parts, freer flowing primaries...the motor doesn't have to work as hard...and then with a tune?

Expect mid to high 20's in the highway, even 30's. I saw well into the 30's...29 all the way to the Iowa meet last year...heads/cam/headers/pulley/LS1TB setup...WB tuned...yeah yeah. It was nice.