@Nyshadow,

I would recommend testing via a wired connection to the router rather than from the testing function inside the router. A wired connection will provide close to the full bandwidth.

I am surprised to see such a large difference and think it may be a bad speed test result. You may also take a peak at your QoS settings. If you are using the built-in speed test and seeing lower speeds, your QoS may be using these settings. You may try to manually set the QoS speed to that which you expect from your ISP. Lastly, check your port negotiation settings on the Archer to ensure that it is using the maximum. If not, you may try a different cable to ensure that there isn't some fault that your ASUS was able to handle. CAT7 cables have to be handled much more carefully as any kinks can drastically affect the connection - its for this reason I usually don't recommend using them, as Cat5E is more resilient and can now handle much higher bandwidth than before.

My team also wanted to make sure that your ONT/Modem is not attempting to manage the network. If you have a Gateway from your ISP make sure that the bridge or passthrough mode is enabled on it - it is possible that your ASUS handled Double-NAT situations differently.