I told everyone it was the fps lagging! I should totally be on the tech team (We don't have a geeky smilie

) Im not sure if I told everyone though.
I'm pretty sure I said this: "The Source netgraph now includes "lerp" indicator which shows the actual interpolation amount (usually 100 msec unless the server or user is forcing non-default settings). The indicator will turn yellow if the server's framerate (actual framerate on the remote machine) drops below this interval." My lerp goes crazy on server 4 (yellow all the time) and I get regular lag, on the other servers my lerp is fine and I don't get regular lag.
Well anyway, apart from my little moment of glory, I'm glad that the problem is known now.