RE: 1 servo or 2 ?
If you are doing lots of high speed stuff, be sure to make the aileron pushrods as short and heavy as possible. Use 4-40 hardware and NO ZBENDS; use ball joints if possible. Also, put the control horns out at 2/5 to 1/3 the span of the aileron to minimize flutter possibilities (1/2 span is the worst possible location). Use stiff material for the ailerons.