I did not have long on my existing plan so I subscribed to the Unlimited plan which will also give me faster speeds 50/20 I think my old plan is about half that, anyho the question I have is :
My existing modem, it works fine, no outages etc, will my old modem work at the faster speed ?,
I am on NBN so none of that changes
Yes your modem will work at the faster speed. The speed you obtain practice is more dependent on the type o NBN connection than your modem.
If you have an FTTP connection you should get the full speed boost.
If you have an FTTN the maximum speed will be limited by the distance from node. If you are within 400 Meters of node should get full speed boost.
If you have Fixed Wireless NBN there are a lot of factors that will limit your maximum speed. The main factor would be the distance from the tower.
With HFC should theoretically get the maximum speed but speed my be limited due problems with the link.