As far as I understand from watching the IRC discussions, it is not slow because of sending the block from node A to node B. It's the actual validation of the block and all of the transactions on each node that is done before relaying the block.
The 0.7 release optimizes transaction validation, so most transactions that were validated when broadcast/relayed across the network don't have to be re-validated when they're included in a block. That will speed up block verification/relaying a lot.