based on the chart 30 minutes to 10k and 60 minutes to 20k @ 10k they wiill be easy prey , waiting a hour to get to 20k the base your attacking you'd have to set up missions for the 29 a hour in advance of the actual attack so they hit with the main force.
There are more a few players that do that stuff. Getting a Lanc to >25k isn't really faster. My own B-17 runs did frequently last 90-150 minutes. I often did fly bomber missions while doing household chores during daytime. No problem spending a hour climbing, I will take a shower, check computer, wash the dishes, check it again, and so on.
And also you can of course take less fuel in the 29. 50% should still give quite some flying time, while significantly reducing time to climb.
