Not really hardware NAT support, but something similar with customized OpenWrt build and last year kernel changes: look at the openwrt-sfe-flowoffload project which I fully recommend and already checked out, that my WDR4300 on Atheros AR9344 is able to handle over 500MBits between WAN and LAN without unsafe/ugly official TP-Link’s firmware.
If you’re thinking about jumping over 300MBps NATing with TP-Link N750 WDR4300 (or WDR3600) with OpenWrt, choose one (or two): 1. checkout that custom OpenWrt build; 2. Overclock your device with custom U-Boot (risky); 3. Go back to TP-Link’s official firmware…
Keywords: TP-Link OpenWrt Download Speed, Hardware NAT, HWNAT, FastPath, FastForward, Flow Offload…
Edit: Since 19.07 openwrt release there’s already support of flow offloading, which gives me easily over 500Mbps NATing DL speed.
Hardware is probably not supported, however fast tests gave me ~5% less performance…