Hugh's weird 5 hourly spikes are rather odd, I had the same thing happen to me when I changed my superhub from 144 to 300Mbps wifi mode, every 5 hours like clockwork the ping graph showed that spike (though not as big as my graph is a lot nicer) and it went away as soon as I went back to 144Mbps mode. Yet another firmware bug? Wouldn't surprise me!
Here's mine right now, I still have the jittery minimum latency, I doubt that will ever go away, though others with US bonding don't get it as bad, if at all.
