hmmmmmmm, interesting,
having added a sony a600 with lense and a small mounting bracket I can say I have noticed a fair reduction in flight qualities, nothing to be worried about, but I would be pretty worried about sticking 3.4 kg under it.
in fairness my sony isnt right on the center of gravity, but its as close as possible without totally removing the VPS, (which I have moved forwards in order to get more space) I know that it will be stressing the rear motors more than the front by adding this weight towards the back, but either way I find 3.4kg to be high, possibly put there in the interest of selling new systems