I have always run 3.91s in my street/strip cars. The car is comfortable cruising at 50-55MPH. Personally on my big blocks, I prefer to keep the Rs at or about 3,000 RPMs when cruising for any length of time. Some guys are comfortable with more Rs than that and that might be okay. But at 3,000, my engines have always been okay. A small block might be good with some more RPMs than that, I don't know because I haven't had enough small blocks to know.