Are you planning to run side cases? If so, you might want to consider the integrated fitment.
I have an old Givi Monokey top box, might be an E46. The issue is that my OEM Yamaha side cases fit so closely to the bike (this is a good thing) that the overhanging width of the Givi top box prevents the side case lids from opening (more than a few inches). Sorry, no pictures handy. This isn't a problem because the Givi box comes off in flash with the turn of key and the press of a button and I avoid packing quick-access items in the side cases.
The OEM top box is narrow to avoid this conflict with the side cases. Side-opening cases wouldn't be affected by a wide top box. My Givi came with the used V-Strom I bought 5 years ago. Sold the V-Strom, kept the box. It's light weight, roomy (holds 2 full face helmets), and has withstood more than its fair share of abuse.
Moral of story - try to plan your whole luggage solution.