RE: RCGF 20cc Gasser
On a 20CC? Why bother? The gas engine is not going to put more of a load on the servos nor cause problems due to vibration.
Heck I'm flying 50CC gassers ( Edges, etc. ) with 130oz/in cheapie analog servos ( $7.00-9.00/ea )and I've never had one fail over hundreds used.
Metal servos tend to wear faster too, until you get into the more exotic range, such as titanium gear servos...
Those I reserve for the bigger planes.