Since no one else has mentioned it, I can't imagine going that far out of the way just for a J seat to LHR. You could save a bunch more money by just flying C+ from the east coast. Fares out of MEX don't really seem all that much cheaper either. 90-day advance Z-fares out of ATL are available from $4K roundtrip and it looks like there's a special in the middle of April for $2900 roundtrip.
Appreciate the thought, I have a short business trip - 5 nights or so. and am able to book in biz based on pricing. The dates are hardset for me and the while it does go far out of the way, the extra MQMs are also intriguing. however i struggled to find flights that fit my short window of travel that would compete with the price of the AM flight (~$4100 RT in I). I can pair a $800 positioning route to get me to MEX from BNA and still do better than most other routes. I belive i can find quite a bit in that range on virgin out of NYC but wouldnt mind a longer TATL to be able to actually sleep on the route over.