Hi Hitech,
>As to the faster with while being heaver, would have to do some big analisis to be sure, but would find it hard to belive that the reduction in profile drag would be greater than the increase in induced drag. The only way I could see this is with a very thick/high lift wing.
I'm afraid my explanation wasn't as accurate as I'd hoped :-)
It's not the wing by itself that causes the effect, it's the fuselage. Angle of incidence is (for example) selected for best level speed at full pressure altitude, so below that altitude, the fuselage has a nose-down attitude at top speed in level flight. Adding weight will require more lift and a greater angle of attack, decreasing the nose-down attitude, aligning the fuselage with the airstream and decreasing parasitic drag.
I don't think the effect has a big impact, but it's interesting for the impact being opposite of what one would normally expect.
Regards,
Henning (HoHun)