How do I ideally configure the radios on the WRT3200ACM?

The default installation leaves me with three available WiFi networks:
88W8887 802.11bgnac, 88W8964 802.11nac and 88W8964 802.11bgn.

With stock firmware band steering was a bust, but I have yet to test it with OpenWRT. I only have a handful of devices that can't connect via 5GHz, so I want to set the bgn network up to connect those few devices.

Will I notice any differences in speed between the other two as my primary 5GHz network?

Thanks all!

third radio, not that great as a general purpose connection.