Hmmmm.... Sounds like a good place for a Ford 9" with about a 3.70:1 gear ratio... Plenty of off the line go power when ya wanna play, and should still cruize down the highway at an acceptable RPM... There are charts and formulas to tell you what ratio to run for a steady cruise at XXX miles per hour to achieve XXX rpm..... As for the speedo gear, they're easy to change out. As a general rule, if you're going to slow people honk and when you're going to fast the police will usually let ya know!!!!!!!