Reviving this thread because looking at the winds at altitude for my planned return trip from KMPV on Friday, it looks like an interesting situation. If I go at 8,000 or higher I will have a significant (at least 15 kt) headwind pretty much the whole way. If I go at 6,000, the forecast winds look practically neutral. But above 7,000, I feel completely comfortable running the engine WOT and aggressively leaned to the point where some cylinders are LOP, others 25-50 dF ROP (even with GAMIs, this is the best I can do without making it start to run rough). At 6,000, running WOT produces enough power (around 70% I think) that I'm not sure this is safe. I'm less concerned about detonation (which Ted has convinced me is pretty unlikely at less than 75% power in an IO-360) than about high ICPs shortening cylinder life. Am I worrying unnecessarily? Of course I can go at 6,000 and reduce power to 65%, but at the expense of a few knots -- maybe as much as 10. Since drag is greater at the lower altitude, my TAS is going to be a few knots less too (~5 or so) for a given power level. In that case, what altitude I choose may end up being a wash. I'd prefer to go at 6,000 WOT and aggressively leaned... IF it's safe to do so.