I voted 20%+ because I run 42.86% higher than the sidewall max. 50psi - SWMax is 35psi. You do notice a significant increase in road noise, but it doesn't bother me. The increase in mileage I have seen is significant enough for me to continue with this much higher pressure. I have seen about a 3-5MPG increase since upping the pressure. Please take caution though, my tires are steel belted radials and you must make sure that your tires are of similar construction because if they aren't, the sidewalls won't be able to take that kind of abuse, and catastrophic failure could result (enormous bang followed by rim on bare ground
).