Ive a Givi 45ltr top box and have had it fully packed and the only difference is that you can feel the rear ends a bit heavier and it just doesnt flick in and out of the corners as well but thats compairing it to having nothing.
Ive got used to it and commonly take a large 3kg chain in the back plus a wear a large 5kg rucksack of books and the bikes fine.
