I could see where a 750 throttled back might burn fuel at a similar rate to a 500 going full tilt...but since I own the 500, not the 750, it's a moot point for me...
Actually, one of the planes I am building is a Mick Reeves Venom. RCJI had a three part review, and they actually flew it with both setups. First with a simjet(I think...anyway, something in the 750 class) and then with the 500. With the 500, by the time all was said and done, the airplane was four pounds lighter at takeoff, and the reviewer seemed to like the model a lot more.

In the end, lighter is ALWAYS better. If not, why do they make high performance engines? Why buy a Jett 50 if you can just stuff in a 60 instead? Because all the weight adds up.
I went through this with DFs a lot...why not just put a 91 into every 45 sized model? Because the same plane two or three pounds heavier could be a very different model.

If I HAD a 750, though, instead of the 500, I would be using that.
Dean, your Hogs look great. I have seen them fly on video, DF and turbine. What a nice, forgiving aircraft. Looks like fun to fly.
I've done that same dumb trick a couple of times on an Me110 twin. Ran out one engine while taxying back. It will only taxi in circles then...

Just finished stripping all the Byron guts out of my JD Models Crusader, will beef it up and put in the 500. What a pain, as I spent thirty hours last week re-installing all the DF stuff after a crash...
Sorry, wrong picture.