If you have nothing else then referring to GPS speed is an excellent idea
Absolutely - if you’ve got nothing else, then you use whatever you can. But Airbus gives me a procedure to follow, and a set of pitch/thrust tables which will establish the jet within a couple of knots of the speed it’s supposed to be at. Sure, we can back it up with a check of the GS, but that’s going to be secondary.
don't forget you are hand flying so its not easy to judge pitch to within 1 degree
Sorry, I disagree. Any competent pilot should have no trouble setting and maintaining an attitude to within 1 degree. Otherwise just maintaining level flight will be a problem, and a raw data ILS will be a bit of a dog’s breakfast.