Our club has gone 4st crazy the past couple of years. I have a Magnum 80 ( soon to replace a 2st .61 in a Tiger 60) and a Thundertiger .91 which is in a Sig 4star 60. There is a big difference in fuel consumption compared to the 2st. But I also have a SuperSportster 40 which has a Thundertiger pro46, and resist going 4st in it. (this is a similar plane to your 4star 40) I personally like the higher RPM and quicker response of a 2 stroke in this size. But some of those smaller 4 strokes are tempting. Good luck!!!!!