OVER: I don't think it's worth getting a 3XL over a 4XL unless you really were going to miss the fingerprint sensor. Like you say, the 4XL has a better screen, newer processor, better camera and will see longer support. Also the 3XL has a horribly ugly notch 😋
My 4XL is purchased from JB HiFi AU and works perfectly on Spark.
Thanks @OVER - appreciate the extremely prompt and helpful response!
I was in Singapore a couple of months ago and there were a few places that had big in-store displays of the 4XL. I got about 5 minutes with one in hand and was very tempted, but just couldn't afford it then as I was on the way home from five weeks in Europe and didn't have enough funds left on my cards to spend on a new phone.