As one of only a handful of riders anywhere who has actually ridden with the new Aqualine tanks on their '09 Berg I can honestly say it is no bigger than the KTM hardparts 13L tank for the EXC's
Remember the front main Aqualine tank is only adding 7.5L (1.9gal) to the bike, and the existing tank stays in place with a good chunk of its fuel still under the seat. The 1.9gal sits on the wings where the radiator shrouds are and a little higher at the fill cap.
So what you get is 16L = 4.2gal...................BUT the tank is only the same size as a 3.5 gal one because there is 1 gal still under your seat in the stock tank
Before my Berg I owned a 525 with the Hardparts tank and used it often, so I feel qualified to compare.
The photos may make it look big, but I tihink being white exagerates that, in the flesh they are not big and are a good fit between the legs.
Check them out in the flesh first before you discard the option, as they give you what a normal 3.5gal tank does, plus an extra 1 gal if you want/need to use it.....................if not fill it less