I believe we always flight planned for 170 true, and it worked out fairly close. 15=17 gph was a good fuel burn, and we had 123 gallon tanks. Same speed high or low, fuel burn got better with height. The one thing that stuck out in my mind about that airplane was it's single engine service ceiling. Practically speaking, we were able to hold about eight thousand on one engine with several people and full fuel. For a light twin, that's pretty good.
Our engines made TBO. We traded for remains, I installed those. The weren't cheap, and they're not getting any cheaper. Those airplanes were hard workers off rough fields and rough conditions, and held up quite well, all things considered.