I am polling the crowd to see what y'all are flying for high altitude XC profiles in NA IO-550 birds. I typically fly 1-4 hr XC lengths and base most of my alt decisions on maximizing TAS and reducing enroute time based off the winds.
That typically puts me in the 7,500-12,500 range VFR. I have portable O2 available, but it seems unless there is a really killer tailwind, my TAS drops off above 10k. Are any of you routinely flying higher? If so, what's in your decision calculus and what's your speed penalty?
As a side note, I hear the PMags or other electronic ignition really helps max power available at high alt. What is that altitude where y'all see the gains?