The IPQ4019 seems like one likely candidate at a modest price-point, as it supports PCIe for a second, 5 GHz card, such as in the EA8300 (supported) or some of the upper-range Netgear "repeater" devices (such as the EX8000, EX7700, EX7500, none of which are supported at this time). The second, 5 GHz radio means you're not sharing time slots between clients and backhaul. (The IPQ4018 lacks both the PCIe and native NAND interfaces of the IPQ4019, from what I understand from this block diagram or from this promotional blurb.)
On the other hand, 2.4 GHz, 802.11n may have better range, depending on your environment, though its capacity under high-SNR conditions is significantly less than that of 802.11ac.
mk24: It's 2 miles, but not straight. I'll use as many nodes as possible to get coverage, but would like to reduce the count from 35 to much less. Because it's an irregular shape, antenna shaping is not really an option. Hmmm. Not sure how to describe this ... think of it as a 2 mile irregularly shaped closed loop in once use case, and not closed in another.
Yes. I have two meshed over 802.11s along with a "legacy" Archer C7. I've had a third EA8300 in the mix from time to time. The EA8300s are running -CT drivers, the Archer C7, being a "Wave 1" device, needs the "plain" ath10k driver for 802.11s support.
I have a similar setup testing somewhere: 2 Archers C7v5 (ath79+ath10k(Wave1)), and an B1300 (ipq40xx+ath10k(Wave2)), and a s905x with MT76 in a mesh.
The performance is not good, and the IPQ40xx device is finicky. It regularly loses contact to the Archers. All of them run snapshots less than 2 days old, and the CandelaTech drivers on all, and the CandelaTech+firmware on the B1300 IPQ40xx.