737 with one wing full and the other empty, at least in the sim, is a non event and not really noticeable for landing. Haven't tried it for real but assume the simulators are accurately modelled.
In the flight crew training manual Boeing have a page or so of text which points out that the limitation is for long term structural protection, and caution crews not to be to hasty to start opening cross feed valves as you may well make it worse than it already is.
Last edited by arcdu; 20th Jan 2015 at 20:00.
Reason: Edited for spelling