FWIW I am now sat in an IB A321 in J. The legroom is significantly better than BA as regardless of what position you sit in there is no knee contact with the seat in front, even when the person in front reclines. Enough room to use a laptop with space to spare too. Seats themselves are not significantly more comfortable but overall this is a better experience from a seating perspective - at least for as long as IB keep their mainline seating like this. IB Express is much less comfortable.