The QoS is reducing your external speeds significantly.
The QoS is reducing your external speeds significantly.
I’m reviewing your setup and the changes you’ve made. The upgrade from 250mbps to 1gbps likely improved overall throughput, but the drop in speed you’re experiencing could be due to how the router manages traffic. By disabling QoS on the fiber connection, you’re allowing all data to flow freely, which might explain why your Ethernet speeds feel much slower compared to the direct fiber link. It’s possible that other devices or applications are now sharing bandwidth more heavily, even though they’re not directly connected to the fiber.
QoS settings place a heavy load on router processors, making it easy to notice increased CPU activity during fast downloads when enabled. This is often visible on the router interface or within the ASUS router application. You might have adjusted the QoS rules recently.
You have an AC58U with four relatively slow cores and a 300/30 connection. On Speedtest, when QoS is enabled, bandwidth caps around 250 MB/s. Turning QoS off allows speeds of 300+ MB/s. In your situation, 2.4 GHz should suffice as the speed limiter for the guest network.
That aligns well, thanks for the clarification. With just two cores now makes sense after reviewing how it operates. If I decide to switch to a completely separate setup using a PC as the router, the issue shouldn’t be too big—especially with a mid-range machine like the one I have. Right now I’m using an older system in the basement that serves as a file server; it’s an i5 7600 (likely around 4 GHz) with 32GB of DDR4 memory at 2666MHz. I’m considering installing Ubuntu or Windows Server there and running a PFSense VM.
I haven't used such powerful hardware for a router before, but it should work well if it has enough network ports. Windows Server will function just like any regular Windows setup. Just note that your router has double the cores compared to mine—your 2 cores have twice the clock speed and should offer better performance.
I personally find the notion of operating a router inside a VM unsatisfactory because it could cause loss of internet access if the host requires rebooting for updates, or a malicious process in another VM might hinder performance. Still, it's a widely used situation so it should function properly.