I have an OS 70FS II in mine and it is an excellent combination - a lot more power than scale. It can be a handful on the ground so getting it quickly in the air is a bonus. This engine runs so well that I ordered another one and have absolutely no idea what I am going to put it in. Your ST 75 should be similar if not a bit more power than my set up so it should do fine. I did have to add some weight to the tail.

Howard