Service Ceiling for a C85 powered 415-C?

I was stopping in Cut Bank to visit friends. So, from Seattle we followed i-90 to Missoula, then angled towards Lincoln MT following MT200 and crossed the divide at Rogers Pass. Then headed North. We ran out of light and spent the night in the pilots lounge at Choteau (really nice pilot lounge with fresh fruit, drinks, and snacks and a loner car), then continued to Cut Bank the next morning. That was my favorite leg of the entire trip, flying over flat farm land with the rugged continental divide, Bob Marshall Wilderness, and Glacier Park, just a few miles off the wing tip.

Understood on the altitude and loadout. And with a DA of +2000 to boot that is good to know! Looks like we have the same prop. Looks like it was a gorgeous flight! Did you fly over Helena or down to I-90 then over?

I climbed to 9500 with a C85 with 48" pitch propeller flying over the Rockies enroute to Oshkosh. DA was around +2000 on a warm calm afternoon when I took off from Missoula heading East, loaded to 1400#. So that might be around 11000' on a standard day. IAS was down to 75 mph, so I wasn't going to get much more out of her. But it was enough to clear the continental divide by a couple thousand feet.

I'm hearing 13,000, Youtube saying 12,000, and others saying 11,000. Does anyone have actual numbers they've flown? If Old Man winter would be kind and give me a sunny day I plan on trying it in mine, meantime what are your experiences with max ceilings? This ties in to looking at long cross country flights with my wife come next spring/summer.