I have a bit of experience flying the SD2 at the altitudes your referring to. I'd say our SD2 regularly outperforms it own performance charts, and will out-lift a B2, but I don't know if we just have an above average engine. I was up to 9,000' MSL a couple weeks ago, but my loads were too light (heaviest approx 400 lbs.) and the wind was too strong to get very near the limits - which is good.