Avoid the WNDR3700v3
Unfortunately, the WNDR3700v3 is significantly inferior to the v1 and v2. It is also a *completely* different design. Here are some of its limitations:
WDS only works at up to 54Mbps.
WEP only works at up to 54Mbps.
It cannot repeat on both 2.4GHz and 5GHz at the same time.
There is no open source firmware available for it.
On the bright side, if you just need a dual-band AP with NAS, it has great range and works just fine with WPA2. Otherwise, if you want a simultaneous, dual-band router with full features and NAS, get a WRT610N.