QDM
I hear what you say, but as a glider pilot I have never even thought of using the GPS for this purpose. I'm not sure it is even capable of resolving ground speed to that accuracy (well my one isn't)
And with my eyesight, looking down into the dark cockpit to resolve a small digital readout and then looking back up into the brightness just seems bad news to me.
I've gone into some short fields, but to me a properly setup and managed approach is what counts, not the numbers
I have flown a Cub into short fields on occasion, but, as I say, it is the view that counts, and with a powered jobby you can always go around, or do a low pass first if you aren't sure.
However, I will bow to your better judgement and experience