Nodes don't just accept blocks. Most of my bandwidth use is on the upload side (sharing data with other peers)! Larger blocks will obviously have a direct impact on the amount of data shared.
Do you run a node or are you just guessing?
i agree.
in stress test, my upload usage explose ... (mempool satured).
(with P2Pool stats, i can view the upload usage)
your node is busy telling every other node about TX they already know about.