There might be a small leak on the expansion tank cap that release more pressure than it should be. So the cooling system doesnt flow properly. KV6 thermostat is different to normal thermostat (look for thread where MHM posted pictures of it) I think I posted all relevant links above and no one understand how it actually works ( I am still waiting reply from powertrain for explanation). Common problem with Hippo. Try to replace the cap first.
As far as I know but I could be wrong there is no remote thermostat for KV6. Correct - although I am led to believe that the 1.8 one would work - its removing the KV6 one that is the problem.
I was thinking of bypass to make the engine even more cooler plus EWP would be great addition as well. Look for thread about HGF. You dont want to cool the engine too much otherwise acid condensation forms within the lower block - just try and keep it a uniform temperature.
I also put Redline Water Wetter (blue) and somehow it uses less petrol but maybe just my imagination. Its only been there for two weeks. I will wait and see. Water wetter is supposed to reduce the water/air barrier and reduce cavitation - a known problem.
Some people cut the under tray to allow more cool air go inside the engine bay. Might worth a try too like you said you not worry about water. I am not convinced more air inside the engine bay is the answer - how about a "reverse air scoop" ie - a vent at the rear of the bonnet to allow hot air to escape and draw cooling air past the engine to cool the rear bank more?
A new expansion tank cap is a good idea - so is replacement with the later type which has a low water level sensor.
Sorry guys - i am still convinced an EWP is the way to go - to keep the coolant at a uniform temperature with the ability to continue to pump after engine switch off - I know its not exactly a cheap option - but neither is a new engine!