this may seem idiotic but I am in possesion of an older fs 91..my great wife bought it 8 years ago and due to illness i had to drop out of the hobby..but oh baby i am back but man so much has changed at least with power..I see planes requiring 90 size four strokes but i suspect that the 91 surpass for instance is more enging that its earlier counterpart..I am debating whether or not to just sell it here and step up to a 120 size as a better allround powerplant for a wider range of aircraft to fly..and if i sold it what is the value as its still brand spanking new in the box with papers etc..I guess i feel uncertain what kind of power an older os 4 stroke would have in a 60 size arf like extra or cap ..I want straight up if possible or at least strong static power to do snappy manuvers.. ok all you experrts tell me what ya think???