I have never been on a British Airways 757. All I can say is that the engines are Rolls Royce and the seats must be dark blue. I'm sure the seat layout is 3-3 in economy and 2-2 in first, like on all 757's.
Do you know that British Airways was the very first airline, with Eastern, to take delivery of the 757?
On their Shuttle service (London to Manchester, Glasgow or Edinburgh)
the seating is all Economy, 3+3. On their European routes there
are Club Europe seats which are also 3+3 but with what looks like more
legroom, possibly better seats and presumably you get a better
service.
Have a look at the seating plan:
http://www.british-airways.com/flights/factfile/seatplan/seatplan.shtml
Of course I'm biased but I'm rarely disappointed flying BA and I fly
them a lot.
I flew yesterday from Helsinki to London in a BA 757. I was surprised that it was very much louder than Finnair 757 with P&W engines. Seating was 3+3 and I found the seats quite comfortable.