After having ridden different kinds... I say fuck a bike without a (big) topcase! You want to ride, go places... you need to carry some things and lock them up when leaving the bike parked.
FZS600 is a rather BIG (looking) bike. So it can carry a big topcase. If it were some small bike, 125, 250 cc, but fazer...
I have a 50+ litre one.
I don't care if it looks big. It is just the right size. 2 helmets, jacket etc. When a woman goes with me it is too bloody small. Told her yesterday she should ride her own bike, so we can carry all the stuff.
Filtering is easy with that one - still not wider than the bike, and rides above rearview mirrors.