Our 421's had the wing locker fuel tank in the left wing, which gives you an extra 28 gals. I've flown the 421 non-stop from Gainesville, GA (KGVL) to Nassau, Bahamas.
We would typically fly ours in the mid-teens, which would give roughly these numbers:
*Based on STD Temp and Lean of Peak (just for you Mini)
10,000ft
32.5" MP and 1850 RPM Power setting
72% BHP
203 KTAS
- Increase TAS 5 kts for every 1000 lbs under 7500lbs.
250 lbs/hour or appox. 42 gals/hour
15,000ft
32.5" MP and 1850 RPM Power setting
72% BHP
211 KTAS
- Increase TAS 6 kts for every 1000lbs under 7500lbs.
250 lbs/hour or appox. 42 gals/hour
FL 200 has the same numbers, except for KTAS which would be roughly 220/225 KTAS.
I would flight plan the 421 for 205 KTAS and 50 gals/hour.
Standard 421 has 206 gals usable, which would provide a comfortable 3 hours and 1 hour + for reserve.
It's a great plane for flying IFR, it's very stable, it handles well and flies pretty well with ice on it.