In joining BA the only people that you care about are the pilots on the seniority list BELOW YOU. Enough on that one.
Anyone holding out for the 777 I can see your point but a piece of advice. If you get offered the 757/767 jump on it like a fat kid on a big mac because its a great fleet to be on. Mixed fleet flying, great equipment and a wide range of destinations. Bidline+757/767 fleet=happy pilots from what I have seen.
Just my take but the key here is get in ASAP.