I'd agree that .44 is wildly optimistic when looking at full power BSFC. In the Lycoming world, .45 is about as good as it gets *at cruise power settings* if you're running a carb'd engine (usually worse, since most are afraid to lean Lycs aggressively).
At 75% power, with fuel injection and balanced flow to the cylinders, you can get a Lyc down in the .42 range, and slightly better than that if you're up high, using electronic ignition that can be advanced, and running at much lower power (under 60%). At full power, a Lyc will be somewhere between .55 & .60. I'd agree with Steve that .55 is about as good as you'll get in a rotary at full power (likely not that good, since we all have butchered Mazda's intake & exhaust technology ;-) ).
With a 'known' engine setup, you can back into HP using Steve I's calculation. But since every rotary has a different intake/exhaust/tune, that makes it a bit tougher to trust, except as a 'ball park' number. With a controllable prop on the a/c, the best way to use the a/c as a dyno is to compare your performance to a Lyc powered model, in climb from near sea level, at the same weight. If the kit mfgr is reputable, they will publish accurate climb numbers for the a/c with a c/s prop, at specified HP, and at gross weight. If you're hitting their climb number, at their weight, you're making very close to the same HP. This is likely to be more accurate than a speed run, since airframe building variations, and even more significantly, *cooling drag* variations, have much larger effects at top speed than at best climb rate speeds.
(Interesting to see so much weight variation in gasoline, from blend to blend. USA E-mogas is very close to US avgas in weight. Seeing almost a half pound of difference between AU avgas & AU premium mogas is wild.)
Charlie