I did a little altitude testing this last summer. At sea level I was peaking at 54.1 mph on the GPS. At 5000 feet, with out a rejet I was reaching 45.3 mph. So using the 3 % rule, I should have lost 8.115 mph or maxed out at 45.985 mph. So I lost an additional .685 mph due to to rich a mixture. That's just over 1.25 percent due to rich mixture. But at 7000 feet it a ton worse and that's why I am going with the Dial-a-jet.