Good research P. I don't work for BA but we are very similar
If 15 to 20 years to SH command is correct (as per Nigel's post,) then I can assume that the seniority list must be equally as large. In which case you will need to consider having no weekends free for years and flying the bid lines that no one senior wishes to fly as they're not popular trips.
To have researched this so well and thoroughly I'm guessing that you're looking to find where's best to spend the heavyweight earning period of your career. If you're in a position to consider it then perhaps a move to the M.E would suit you better at your age.
If all goes well, there's a high probability to become a skipper on a 330/340/350/380 or 777 within 6-8 years. Although its London prices out there (so nothing new to me) there are very, very few bills to pay with friends of mine earning large sums of tax free money with only a mobile phone and internet charges to pay for as a regular outgoing. (I'm sure you have friends out there as well.)
With the UK coalition govt. cutting middle class benefits, taxes rising and general costs rising like petrol, house and car insurance, it could be a good time to move.
Horses for courses I guess.