1. MAP gauge reads .2 in. low. Certainly when the engine is not running and, as far as I can tell, always.
2. 11 GPH vs 10 GPH at high cruise (2400, WOT, 7000 ft. PA, 6700 ft. DA) might, maybe, possibly, be worth 1 knot (144+/- vs 143 +/-. But it does knock 15 deg F or so off CHTs. (One needs to be very patient getting these measurements, given that the air refuses to be super-calm.)
3. The fuel gauges will actually give you gallons readings even after passing the "Lo" annunciation. Basically it alternates between the two displays. My motivation here was to drain a tank so I could find out what it really holds, as I have a suspicion the tanks hold a bit more than 20 gallons per side. I took the left tank down to where it said zero, kept it up for a bit after that, then chickened out and switched tanks. (I once had an enlightening experience running a tank dry in flight in a fuel-injected Comanche
)4. The plane will run quite a long time on my left tank (to be precise) showing 1-2 gallons. Even at zero, it kept it up longer than I would have thought. I could have been tapped into unusable fuel in this region, as it was nice, coordinated straight-and-level flight.
Next step: Note what the left tank actually takes when I fill it. (I don't refill before putting the plane up after the flight to avoid having fuel expansion fill the hangar with flammable fumes.)
). But I was able to drain the last of the usable fuel out of it (after running at zero gallons indicated for a very few minutes) and measure that remainder. The procedure was to select the left tank then let it drain it out of the bottom of the strainer into a measuring cup. Out came just over half a gallon - more specifically about 4-1/2 US pints. So the fuel level indication was accurate enough for operational purposes.