I've had this B&R rolling computer bag for a few years and love it!
http://www.briggs-riley.com/category...ng-Brief_KR305
This may be slightly newer model of the same bag --It fits everywhere -- under seats, in all overheads, in the sizer at LHR, never a problem. And it rides above any B&R rolling carryon on the handle perfectly so the weight is not much of an issue.
You should be able to get it at a much better price than the quote on the B&R site -- either online or at a B&R dealer. I think I got about 40% off on mine.