At 60-70 tanks, it's probably time to adjust he valves again. I like to see 9500 on my 72. What's your altitude? I'm at 4350 ft and a 12-6 seems about right. A lot depends on what you fly and how you fly it. If you like the way the 13-7 flies, why change? At < 75 tanks the engine is FAR from being worn out, if that's what you're asking.