600Mbps was a figure I pulled out of the air a bit but I'm pretty sure I have seen someone topping out around there with PPPoE - looks like you are on IPoE (DHCP) with Stuff Fibre though so the router may handle that a bit better - that is a reasonably common thing to see. Netcomm are a shocker for it for example.
As Hio said, very likely you are running into a CPU bottleneck on the laptop. I see Stuff recommend that router so you would think it would do the speeds they are advertising, but even so doing a speedtest from within Windows is not an accurate way to test.


