sorry, I made things confuse. There is no filter from wall socket to my Sagemcom NBN device (I just checked again). The cable from wall socket to my Sagemcom device is using phone cable, not UTP. There is no NBN fibre cable to my house, also no NBN box in my house and I reuse the existing phone socket/plug as before (ADSL2+).
What type of NBN is this and do I need VDSL capable device if I want to replace Sagemcom?
FTTN is definitely the slowest of the wired NBN tech, and the speed will be due to a combination of distance to the node, quality of that line, and quality of the home phone wiring.
Here is an old map with distance and speed estimates (read disclaimer on page) which may or may not give some insight.