IO540, if you're going to make it that complicated, then you'll need to specify whether its FP or CSU, since you can maintain quasi-constant BSFC with a CSU, but it will degrade more rapidly when reducing power with a FP propellor.
edit: actually, I don't think it will make any difference to my badly drawn graph, since the only thing that will change is the shape of the drag power curve (OK, you'll need to re-label that as SHP to be strictly correct). I think the curve will only change subtlely - not enough to make my diagram any more inaccurate.
The main point is to demonstrate the effect of a tailwind (in this case), where GS > TAS