PS how fast is the topbox rated for ?
Yes, it is a big bugger.
That top box was a free sweetener on my white K16, was then sprayed red for my second, then black for my third which happened to be the same black as the fourth and then my latest. I takes two helmets, is central locking, has two dampers that slowly open the lid and a built in light (no USB or 12v socket though). You have to unplug it from under the back seat and it is not really designed to be constantly put on and taken off and doesn't have a carry handle.
The K16GT doesn't come with a top box and it is an optional extra, but I have run some big speeds on Autobahns one up and two up without any problems. The K16GTL comes with a top box that sits about an inch or two further back and also has a bigger screen and softer suspension - that model is restricted to 139mph.