I was in the same situation as you. Same Router too.

I could actually get close to 1 Gbps with the stock firmware. But it was unstable, requiring a reset every other day. I used an open source firmware, but it didn't contain the NAT offload module, so I would not be able to get over 200-250 Mbps. (This was is all wired, not wireless).

Since I had a wifi access point, I ended up switching to an Ubiquity Edgemax router and haven't had any problems since.

Not really a fan of TP-Link.