Mine has just run with its new underseat system made from a 45mm 916 std set. Not sure on performance gains as yet, Tho i doubt any are to be had as the valves limit the flow not the exhaust size.
It isnt too loud either considering we have made a 20cm Carbon underseat pipe for it.
http://www.barcroftmotorcycles.co.uk/DD/8.jpg Glyn
[Edited on 8-2-2006 by Scooter916]