I have an R600, R700, and R710, and I can confirm that the R710 has noticeably superior coverage. It seems to be able to deliver similar speeds as the R700 through one additional wall. The major differences for the R710 over the R700 are that it:
- has more BeamFlex elements for forming more antenna patterns
- Has 4 radio chains (4x4:4) which presumably improves antenna diversity
- Supports 802.11ac chip-based beamforming (e.g. 4x4:4 can make a 2x2:2 beamformed signal) in addition to BeamFlex
- Has a much better RX sensitivity than the R700/R600, which permits it to hear clients from further away.
But to be honest, the R600 is still a star for cost:performance ratio. And if you ask me, would you have 1xR710 or 2xR600 for a given deployment, I would lean towards the latter, unless you are truly out of channels due to high-density deployment and improving the AP is the only way to improve performance.
Can you elaborate what your performance concerns are for your R700 APs? What kind of clients are you serving, what performance are you seeing, and what kind of performance are you expecting?
It is peculiar that with 5 AP's, you are simultaneously concerned about 5GHz coverage *and* number of channels.