Not any Lancs yet but have been trying to hunt 17s and 24s. But when they're at 30K the 51 is useless. That's when I started checking into the service ceiling of the 51D. It appears to me that the service ceiling for the 51D is around 30K in the game and not the 41900K listed from outside sources.
Maybe there's a difference between official service ceiling and (perceived) practical usabaility at altitude? They don't necessarily have to match exactly. And keep in midn that bomebrs do fly faster here than in RL at any altitude.
That being said, the 51D is far from useless against enemy bombers at 30k. I have killed quite a number of bombers at that alt (and even more, eneyy interceptors, because traditionally I have used the 51D more for hi alt escorts than buff hunts.).
There are, of course, fighters better suited to combat at 30k and beyond, like the 47M or the Ta 152H, both of which had a higher service altitude than the pony in reallife.
Oh, and on the Lanc, the days of Lancasters doing 30k bomber runs with full bombload on a regular base are long gone since HTC did some adjustments.