@mouskowitz 

Go to Advanced > QoS > Application Priority, make sure Standard is chosen.

Go to Advanced > System Tools > System Parameters (bottom left), disable "Enable WMM".

Finally, while still at the system parameters menu, scroll down, and make sure "Speed & Duplex" is set for 1000Mbps Full Duplex. 

@Tony I have a similar problem with C2300 (EU, ver.1.1) - both the Wi-Fi and wired connection speeds from the C2300 are stuck around 198-206Mbps. Wired connection passing by the C2300 constantly delivers the providers` promised 500-550Mpbs.

The above suggestions around QoS, WMM and  "Speed & Duplex" do not help at all - even more, disabling WMM on 5GHz network slowed the speed down to 28Mbps.

How can I get the full speed from my C2300?

@Kuriozs 

Speed issues are not always Router caused, especially if you get full speed via Ethernet cable.

For instance, I have a PC that I can use wired or wireless. Will use wireless most of the time over having a cable run along the baseboard.

Here are my specifics (and an Archer A20 but that has nothing to do with my PC speeds, and the A20 tests ISP speed @ 478/23 if that matters):

ISP speed rating, 400/20Mbps overprovisioned, usually 15 - 20%

PC, wiired with CAT6 cable on 1GB router and PC ports, 480/23Mbps.

PC, wireless, with a USB 3.0 AC1900 adapterd (2.4Ghz 600Mbps, 5Ghz 1300Mbps capability)L

 --  Speeds depends on 'how' the USB adapter connects to USB Protocol on boot:

      - 3.0, 480/23Mbps

      - 2.0, 250/23Mbps

My USB 2.0 speed is limited by the USB 2.0 transfer rate, 250Mbps. Yes, the CONNECTION speed of the USB adapter IS 1300Mbps, even under USB 2.0 Protocol.

Wireless speeds can vary by many factors, and change with distance from the router.

First question is what is the 802.11 wireless speed rating? G, N, AC?

2nd one, did you forget to DELETE the old CONNECTION and create a new one? Problems can happen like you seem to have if you do not change the connection.