Hi mate, are you sure its flowing correctly? I aint a mechanic but how has he tested that its flowing too fast? it should be cooling it too much not heating it if it was flowing too fast.

The uprated fan switches come in at a higher temperature to cater for the heat sink on the alloy rad tanks, which points to it heating up too quick/flow problems.

It might be worth taking the radiator out to have a check its not blocked by a radiator specialist. The standard ones collect sludge in corners where the fan switch sits. I would also considering checking the thermostat again by testing it by boiling it in a jug to rule it out, I have purchased new ones before that havent opened correctly. And lastly if the water pump isnt new might be worth checking the vanes havent disintergrated and that its a proper cossie one and not a sohc one.

Also if you can get a heat temp gun, you could try point it at rad / expansion tank to figure out where its hot / not hot.

Hope that helps,

Kane