I've been able to collect more performance points over the last few months as TH has made a trip to Wisc (not Oshkosh) and east to St Augustine. On both trips I've been able to get to 7500 and 8500 feet. At those altitudes I'm still able to get 82% calculated power. The fuel burn is a little higher as the cylinder head temps on #2 rose to 400 degrees. I found that the front baffle material had blown forward and I lost my efficient cooling. I've made new baffles - an inch longer and that should solve that issue.
But back to performance. With 2500 rpm set and 24.5 inches at 7500 feet, my GRT display shows 164 knots true @ 8.9 mph. I'll lean more aggressively now that my baffles are happy and see what better fuel numbers look like.