How have you fitted them to the Givi racks, have you put strengthening inside to take the weight and what locking mechanism have you got?
What size is that top box? surely it must make the front end feel very light. I had a CBF1000 GT full touring kit, anything above 60/70mph you could hardly feel the front end on the deck. Made me very cautious especially in the wet and especially on roundabouts were the road surface is usually polished.