We have 1080 useful. I can put 103 gallons, bags, and me and the wife on board. If your guy has 750 then something is wrong.
I can run 27" and see basically 231 performance on 15gph or I can run 31" and run faster. I can climb out at gross 1750fpm. Kind of handy departing a short strip at 10k density altitude.
The 520 doesn't cost me much to mimic a 231 and the rocket cooling is much better, climb is better, and I can run 230-235 knots if I want to.
The big bore mooneys are much more flexible.
It cracks me up to see people spending 20k or more a year to keep a plane then bitch about a few gallons of gas.