Just two small points with the GIVI top boxes (of which I am a strong advocate, having had one on the back of my K100 until it left me, with the bike, via TradeMe).
They can raise the c/g of the bike a lot, because of the packrat tendency we all have to fill the (large) space available with goodies.
Their aerodynamic performance ain't necessarily the equal of BMW's - on the old LT above (insert number that would surely get Steve Bell's attention during work hours)kph I could always feel a bobble at the back of the bike where the air coming off my helmet and shoulders hit the top box. That one had an easy fix - always carry a pillion.