I'm due to fly BA112 (6:30pm departure) on May 5th in WT on a basic economy fare. 5 days ago, I got an e-mail from BA that changed my seats due to a swap from 747 to 77E. Today I get an e-mail from BA saying that due to the equipment change, I am eligible to change my flight to anytime between May 1st and May 19th. I prefer my current flight. I have a separate ticket for BA700 (LHR-VIE from T3), so my current itinerary gives me a 3h30m cushion to make my connection. When I was booking, I also considered AA100 (6:10pm departure) which would honestly be better (better JFK lounge, arrive in T3) but with no seat selection on a basic economy fare, I opted for BA112.

I don't have access to ExpertFlyer, but it looks like the first three evening BA flights on May 5th are completely full in WT. Do you think my chances for an OP-UP are higher if I stick with my current flight? Or would my basic economy ticket put me lower in line despite my status?