Most of my experience is with Givi, on my past 4 bikes. A Bandit1200, SV 650, SV 1000, and now my 05FJR.
I use the trunk daily and try to keep it mostly empty to store my helmet in when I'm off the bike.
If you will have a pillion, get the 52, the 46 is snug to get 2 helmets in. :)