I got both the TT61 and the ST G90 ... TT61 is a great little thing, runs well and is trouble free. ST G90 is a great power house and not a screamer, takes a while to run in (mine was a well behaving engine after 2-2.5 gallons). If I were you I would go for the ST G90, its not expensive and will last a long time (so I have been told many times). With a nice 15x6 prop your 4* will just reach for the skies in a vertical! Oh yes ... my G90 starts easily and idles very well.