Packet loss is hard to guess, but internet latency you should probably plan for up to ~750ms, though the vast majority will be under 500ms. The biggest outliers are Australia<->US pings and satellite internet. Depending on your target market maybe you can ignore those. If you are doing stuff for mobile devices it can be even more unpredictable. As a random guess for packet less I would say to plan for somewhere around 1-5% at the most, generally we see much less than that (~0.1% at the worst of times) and usually that is only on UK<->US links at peak hours (UK peak that is). The packet loss itself isn't a problem, but throw the transatlantic latency into the mix with TCP retransmission and you get a very jittery connection and can have trouble managing network buffers (this was for file transfers, for lower data rates I doubt this would be a problem).