You should take the camshaft into consideration, too. There is an operating range listed with most cams. In my case it is 1800-6000 rpm. I have a 700 R4 with a 3.89:1 rear gear and 30 inch rear tire. I cruise at 2200 rpm in overdrive at 70 mph. Around town, I drive in D rather than O. It will do okay at 1500 rpm in slow traffic, but regular driving, it likes 1800 rpm and above.