For what it's worth, I commute with the Ortlieb Sport Packer Plus panniers and
my 15" MacBook Pro will fit if I put it in "top first". It's tight, but manageable,
since I only take my laptop to work once a week or so. If I had to take my laptop
every day I would look for a slightly bigger set of panniers. Otherwise, I really
like the Ortliebs.