It seems a problem on all VR routers because my VR400 has the same situation here. I have a beta firmware to fix it. May be you need to ask them for a beta firmware of your VR600?

Same opinion with Dlink that it sounds like a 1MB issue. How about set Bandwidth control/Qos to restrict the upload speed?

Mr Dlink has shared the details,so there is only one more thing i want to say is that VR600 is full Gigabit ports while VR400 only has one Gigabit port.

I think D9 should be the same with the the other Archer routers. Did you have a power supply for your HDD?

That seems the built-in Speedtest interface in VR2800 is unavailable, you could contact TPLink support and i think they will have beta firmware for your issue.

Hi , i think you only need to set a virtual server for port 1723. Do not need another firewall rule on router. And the most thing i think you should pay attention to is the firewall on your server....