Whopity, I take it there was no wind so that your GPS ground speed matched your Target IAS?
But I agree power and attitude are the primary references, although to try to answer the original question, is GPS better than nothing? well if you can get a wind speed and direction from ATC then you could calculate a rough target ground speed from which to fly an approximate approach speed, but I would not rely on it very much!
Last edited by bingofuel; 27th Dec 2011 at 20:42.