The first poster discovering the client-block-receive to miner-long-poll-receive delay time reveals another factor unrelated to the Bitcoin network block propagation speed - the time it takes for a pool to transmit a new block to all miners. In my past experience, depending on the number of pool miners, the number of pool servers, and the pool software and it's delays communicating with Bitcoin, going through the list of miners and sending each a LP response can take a significant amount of time, generally four, but up to ten seconds from the first to the last miner being notified. This from my own research profiling pool LP times as a predictor of who found the block.