The difference between the W fare I'm in and the V fare needed for the promotion is $118. The mileage LAX-LHR is 10,912. I suppose that is around my breakpoint, used to be 1.5 cents per mile, but now is lower, given Chapter 11 discount.
Can't complain about my upcoming booking; $408 RT LAX-LHR, with sweet spots putting me and wife in Biz.