Not sure if this is helpful, but if you are one of those newfangled smartphone users, you can set up your gps location doohickey to give you exact mph, then put a tach in your vehicle, and feel your way to a comfortable number for you. These engines are resilient and can take a lot of punishment, but if you 'feel' you are pushing its limits, you probably are.
I really like the addition of a tachometer. Cheap, easy to install.. + to positive, - to negative, and green to the minus side of the coil. You will never wonder how hard you are pushing the old girl again!
