Thanks for the compliment, B. I am looking at a 255/45/18 because i have rims to fit. 26.0 diameter. You may be right on the 3.55s not hurting much. At 120 mph the rpm would be about 5800 given 6 percent slip.
I do have an idea for a cold air package. Using an old air cleaner base and top, i can form a duct to a cone type air filter down low by the valance. Might help a lot.