I think your first order of business is to do what a lot of people are doing right now: trying to digest the entire "Avios" award chart that BA has rolled out.

Depending on what your desired award goals are, you will range anywhere from loving to hating the new system.

My hunch is that out of London you're going to stick with BA. Airlines always treat their own elites better than alliance elites. Sometimes it's overt - they design their websites so that "native" elites have an easier time seeing preferred seats, upgrade availability, etc. Sometimes it's just the softer elements like service at the airport, potential for operational upgrades, etc. I've had a few situations over the years where I was Star Alliance Gold but the partner airline I was on that day didn't automatically see me as a Gold. (I literally carried the little plastic card to prove it to lounge agents on occasion!! )

BA is advertising that 97% of its awards ex-LON are the same or less costly now than they were on Nov. 15. No idea if it's true, but go read the BA board and get some opinions there. Look for opinions from fellow Londoners: those of North Americans or continental Europeans might be totally different because of the way the new segment system works. You're less affected by that, starting in London.