I use a Givi Maxia E52 (with the optional highlevel breaklights), with System panniers - works for me! Used every day for commuting - keeps the bike narrow enough and I tend not to notice it....
You do have to sacrifice the grab rail for a standard install (although I believe some have mounted the Givi rack further back), but you can pick up a BWM grab strap which mounts between the seats (for 1150 GS dual seat!).
Steve