Hey Knightrous, I tried that briefly but didn't see any result.  I'm thinking that you are on the right track though, I will give it another go.  The S2000 water pump was never designed to pressurise such a large system and move that much coolant, so kinda makes sense.  I have been pricing the davies craig electric water pump kit for $350, I definitely wouldn't have this issue if I installed that and removed the thermostat.
 
I would prefer to avoid electric though, if they fail it is sudden.

It does sound feasible doesn't it?

Thanks, I just bought a 150lpm davies craig pump but am looking into setting up the pump/fan controller and removing the thermostat.  If I clip the impeller I can keep the same belt but am considering removing the factory water pump and blanking it off (with a water intake pipe of course).