Gargoyle does not currently support v4. OpenWrt is close to having proper support in trunk/development builds. Gargoyle won't have support for it until it moves to that branch of openwrt.
excuse me for reviving this thread but i also impulse purchased this router. the stock firmware is quite annoying and besides i'm used to gargoyle gui now and cannot take it anymore. please include the wndr3700v4 for support for the next release. please... i found this over at the openwrt forum