Thanks netwrks,
As I suspected, one AC-PRO will not replace the RT-AC68U. I had HOPED that because I could ceiling mount in the optimal place (that I cannot put a consumer router,) one AC-PRO would do, but indeed (as I was told) it is not as powerful as an ASUS and is not as good as a replacement. Let me be clear that I get usable coverage in almost all of the same places, but the throughput falls off pretty quickly when I go past more than one wall unlike with the Asus which is getting much higher performance at those places.
In addition to that, I have after market high gain antennas on the Asus router
https://www.amazon.com/gp/product/B00KQ0EN2A/?tag=snbforums-20 which make a profound difference in range, especially on 2.4 and almost annoyingly so. I can see my SSID half way down the street (even though it's not usable.) I really should turn down the 2.4 power (I'm gonna get on that.) Those antennas really do actually greatly help 5Ghz range as well which is really the only thing that needs help.
There's a tip, if anyone wants to boost the range on an Asus router, these antennas have served me well.
With the stock antennas, the coverage is a lot closer to the Ubiquiti but consumer blasters are what they are is still going to win.
So because of these massive antennas, it's not really a fair fight anyhow.
The Ubiquiti is not supposed to win, though. As Netwrks indicates, they are really designed for a lower power distributed network and indeed if I were to place 3 in my house, I'd probably have a minimum of 350Mbps 802.11ac on iDevices at every inch which sounds pretty awesome.
As it is now with the Asus, I get at least 150Mbps in the worst corners spots of the house after I moved it to a slightly better place (still not the best place) but 200-400Mbps in most areas, which is about the best you could ask for.
That being said, I've determined that due to the chicken wire in a formerly external wall (that's part of an add-on room) it's impossible to have one single best spot. That wall acts like an RF shield so no matter which side the AP is on, it's going to bet less than optimal on the other side and there's going to be a couple of rooms where it's just so-so. The ASUS is as close to that best spot as possible right now.
So goes the dilemma. I've invested $200 on a Ubiquit AC-PRO AP and cloud key. I either need to add at least one more AP (two will probably suffice) or go all the way to 3 and I'm done. I should never have to run these experiments again. If I stop at 2 I might end up placing them, then re-placing them again so why not just go to 3 and finish.
On the other side, I could stick with the consumer blaster. I mean, it's working. It's actually fine. I'm kind of fixing something that's not really broken. But being the nerd I am I'm obsessed with best performance especially since I got Gigabit Xfinity and want to squeek out every bit of performance I can.
The nice thing about one consumer blaster is this is that every few years I can drop $200-$300 and get the latest and greatest single piece of hardware, especially if I can use these high gain antennas. I was initially looking at the Asus 86U (which I don't even need.) If I ever want to upgrade the Ubiquity I'd probably want to upgrade all 3 APs at the same time and that sounds like 3x the cost but the APs are not really that expensive each. Right now I can get a AC-Pro locally for $125 and the 4x4 mimo model is prohibitively expensive at the moment but should be a lot cheaper in the future when and if it ever matters. I don't expect to have anything that does better than 2x2 MIMO for quite a while anyway.
So Ubiquiti's stuff is very nice and I want to go all-in. I love the idea of having the APs independent of the router (and might get Ubiquiti's router.) I'm just making sure I'm not sinking a bunch of money into something that's not necessary and essentially replaces something that pretty much already works.
I guess my plan is to put one in the hallway covering the bedrooms, one in that "add-on" room that I refer to as the "Faraday cage", and another near the front door near the entry way. That'll give me near perfect 5Ghz range to all areas.
In the past I had avoided multi-AP setups because it seemed like clients always hung on to the wrong one and dropped when roaming which is why I have two Asus RT-68Us, I had a dual set-up for a while that I abandoned. But the Ubiquity stuff is designed to be a multi-AP network and should not have that problem if I configure correctly.
Sorry for the long wordy post.
I think the conclusion is that I'm going to get two more Ubiquity AC-Pros to do a 3-AP installation. I like the idea of having 5Ghz APs distributed everywhere for max performance and this Ubiquiti hardware is pretty cool.
Final conclusion. Since there are really only two 80Mhz channels for 802.11ac, how do you configure 3? Just keep the power levels so they don't interfere too much and put the 3rd on the other channel?