^ Perhaps its just a limitation of the device itself and you may not be able to achieve it over wireless with that device. I have a D-Link 825ACG1 router and over the 2.4 Ghz wireless N, I get about 80 Mbps or so and over 5 Ghz wireless AC about 250 Mbps plus.
Other options you can try are, changing the wireless channels, see if you can make it different from your Netgear device and choose one which works best for you. (as you said you keep both devices online as backup)
Also on your Netgear WNR614 device, what is the actual speed you get, I mean if you do a speedtest?
In netgear I get about 87mbps actual internet speeds and as it's a shared line to rate is about 9mb/s.