I have tried lots of plugs, but getting European plugs is a problem here. I know a fair amount about 2 stroke plugs, but don't have a clue about the 4 strokes, what heat range they are, how much platinum they have, exactly how they retain their heat from cycle to cycle, ect. All the 4 stroke plugs I have tried run well on E85 (except the Fox brand, which runs poorly). The big problem is that they all die fast when used in a 2 stroke engine. I guess they can't handle the extra power, the coil breaks after a few flights. The Thundebolt plug I mentioned is the only one I have tried that does not burn out after multiple flights. It is advertised as a "4 stroke and 91+ 2 stroke plug", so I would look for a European plug that has a similar description.
Wrapping the head with an insulator is important as well. Measuring the temperature I see that the engine will not run reliably until the head is at least in the high 200's F, and the plug heater has to be kept on much longer than with methanol fuel as well, adding further stress to the plug. Starting the engine is difficult in temperatures below 50 degrees F. I squirt a little pure methanol into the carburetor for starting to solve the problem. Once the engine is heated up, it runs fine, I don't have any dead sticks anymore, and the needle valve sensitivity is much less when the engine is a stable high temperature. I highly recommend getting an infra red remote thermometer to figure out how big a baffle you need on your particular engine cylinder head.

Good luck!