I can't give you advice on what gear to change to, but I'll give you this (apples to oranges) comparison (and I'm sure you have a car with OD too). My 2001 Dodge truck has 3:55's and an OD transmission, and it turns about 2.200 RPMs at 80 MPH. Spending your money is easy, but if overdrive is in the budget, check it out. I think you'd have all the performance you're looking for...