In Bitcoin the PoW mining has very little overhead in terms of bandwidth. The miners simply need to produce the PoW, which I believe is 32 bytes per 10 minutes.
In Casper I understand every validator can vouch for a block by signing it. Assuming the signatures are ECDSA with 80 bits of security, then each signature is 320 bits. If there are 1000 PoS nodes signing each block, that is 320,000 bits (40kB) per block.
If blocks come out every 17 seconds that is 84MB every 10 minutes, several orders of magnitude above the 32 bytes per 10 minutes in Bitcoin.
Are my numbers correct/reasonable? What is the expected network overhead for Casper's PoS mining? Does this affect blockchain bloat?