0.4mm is fine for the UK. With 0.3mm we are currently finding the engines are still running very rich at 260deg F. We are needing to go to 0.4mm and lean the engine out to get the perfect settings at 230 -240 deg while maintaining 7 - 9 minutes runtime.

With 0.3mm the ideal running temp was 350degF. The only problem we have at that temp is that the big end bearing cant withstand it for long unless you are running ceramics. While the engines were comfortable running that type of temp over a 5min qualifier I wouldnt like to maintain it with any engine over a 30min Final.