We've owned all 3 types of Onan and your numbers are pretty close to our experiences. I like the propane the best, it's the quietest and least finicky, but it uses the most fuel. The gas was my least favorite of all 3....
Bob & Sharon
2019 Winnebago Travato K (2018 Chassis)
Past RV's: 2013 WGO ERA 70A, Chevy PW Lexor
Itasca Navion, 29' Jayco 5th Wheel