According to the product page of the TP-Link Archer C2600, it can handle up to 800Mbps over 2.4Ghz and 1733Mbps on the 5Ghz band. So, you router doesn't need to be replaced. You're upgrading your modem which is all you need to do, as it most certainly is the bottleneck at only 300Mbps. https://www.tp-link.com/us/home-networking/wifi-router/archer-c2600/

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