I have the large Odssey top box on my f650gs. the top box produced less drag than my 10 inch Odessey saddle boxes...a lot less. I often carry up to about 25lbs in the top box....it does not seem to bother evan at speed of a 100 or so.
Having said all this being ok, I fave to note that puting weight up high behind the rear axles is the worst place to put it on a motorcycle.
This just points I don't always practice what I preach.
ps You have a fair amount of flexibility on how forward or how far back you mount your Jesse top box. I very seldom carry a passenge so mine is more forward.
I don't think you can go wrong with Jesse stuff tough and dry