If you can get back on a non-codeshare (i.e. a flight actually operated by BA) then I would do so. IB is ghastly. I avoid them if at all possible - even to the extent of taking less convenient BA-operated flights when I need to go to BCN/MAD.

No seat requests or pre-assignments in Euro Traveller for anyone, even top tiers! The only pre-assigned seats in Europe are UK Domestic (Top Tiers/Fully Flexible tickets) and Club Europe (anyone). Seat pitch 30-31" on BA. OK for these fairly short flights. Your best bet for a good seat is to use Online Check In (search this forum for 'OLCI' - lots of references to it I should imagine) at T-24 hours from depature (another advantage to avoiding crappy IB on the way back - you can only OLCI on BA operated flights).

Phil