Brooke, I doubt any Lancasters will survive against anything later than 43 Luftwaffe.
I think it can depend on the ratio of things.
To take two extreme examples, let's say there were 20 P-51's and 5 Lanc formations vs. 40 FW 190A-9's. In that case, all of the Lancs would die every time short of target. Let's say there were 20 P-51's and 40 Lanc formations vs. 20 FW 190D-9's. In that case, a bunch of Lancs would survive to target.
What I try to do in bombing scenarios is choose the number of attacking fighters, number of attacking bombers, and number of defending fighters so that the defenders aren't overwhelmed and have their chance to kill a fair amount of stuff, but the bombers won't be totally wiped out all the time. I try for middle ground.
The problem is that you can't calculate that perfectly and guarantee it. The best I can figure is to look at past strategic bombing scenarios (Big Week, DGS, DGSII, BOG, BOWL, Final Battle, etc.) and look at various ratios of things that worked out OK, tweak it some for circumstances (like you might make them more accommodating to the bombers if you have Lancs instead of B-17's).