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Sounds like something you'd likely need to gather for yourself. I don't know of an open source that publishes latency between nodes on the btc network. To do this you'd likely want to set up many full nodes around the world, sync their clocks as close as possible then just log all of the tx that enter the mempool and their tx time.
By far the easiest way I have seen to realistically use bitcoin is to buy gift cards for a specific retailer using gyft. Although it is more convenient if you find someone that is willing to sell you items for bitcoin.