In the A320's fixed-thrust mode Open Climb the aircraft will happily allow itself to get 20 knots fast or slow. In a mode such as V/S where the FMGS has flexibility in both pitch and power it does a much better job of maintaining it's targets. In the "soft" Alt Crz mode it stays within 20 feet of the selected altitude. Heading is easy, and deviations are imperceptible. On an ILS the needles are glued in place, airspeed within 5 knots unless it's gusty.