Straight water offers the best coolant but will corrode the system so any antifreeze that contain agents to lower the freezing point and have corrosion inhibitors in them will not cool as well. A compromise of 70/30 mix will split the hairs between a bit better cooling and still offer corrosion protection but not for as long. To me, it's not worth the trade off so 50/50 it is. If the engine is running too hot, it's not the coolant but mechanical in nature. Claims that lower the engine temp are mostly BS.
Regarding the EVANS, I've flown with it and the only difference was it didn't expand as much and showed a lower water pressure on the gauge. Engine cooling on the Rotax was not noticably improved.
Ron