Newer Netgear firmware (1.0.9.64_10.2.64 and newer) prevents GUI downgrades, preventing DD-WRT installation (K3_R7000, build from 9/23/18 file has a lower version number, 1.0.5* that Netgear disallows). factory-to-dd-wrt.chk for normal builds.chk (trailed) file using the Netgear web interface *. Both are compiled from the DD-WRT trac SVN, but Kong builds are deprecated (see Documentation for differences).
The primary Brainslayer and alternative Kong build links can be found in the Firmware FAQ. OEM firmware uses Broadcom's proprietary CTF (Cut-Through Forwarding). SFE accelerated NAT was added to DD-WRT since build 33006 (kernel 3.10+), which Kong tested at 900 Mb/s throughput (download and upload). The dual core ARM CPU is beneficial for running multiple simultaneous services on the router.