All I've ended up doing is putting everything back to normal, by that I mean deleted port forwarding for the PS3, made sure uPNP was still switched on in the SH, increased the advertisement to live hops from 4 to 11 in the SH, and let the PS3 connect in auto.
Turned off the SH once I'd made the changes for 30 secs then rebooted it, then booted up the PS3 and it seems ok to be honest.
Just out of curiosity how much Jitter do you get from
http://pingtest.net/
Have you got any FP attenuators on the SH