Flying with a RC Glider on mountain's slope is a nice sport and a genuine technical discipline. We use the brushless electric motor only to rescue the model.  Piloting a RC model is very similar to brother in scale 1:1 glider!
Following the wind's condition on slope, we use differents types of RC models from 1,5 mt to extra large 7 mt wings in scale 1:2.  Normally a range of 2,5 / 4 mt. wings size is a good choice for a RC Glider on slope.
I have 4 RC gliders in my hangar, starting from 2 mt to 4 mt wings and from 500 gr to 6 Kg weight, with and without electric motor on board, my radio is on standard EU analog frequency.