From own experience with the 860L:
You will not have a very huge problem on 5 Ghz, just your overall throughput on 5 GHz will be 50% of what is possible without the bug.
You most likely will have huge 2.4 problems when running USB 3.0, the software bug fix does not solve 2.4 GHz problems, this is a general USB3 hardware standard problem affecting many access points (as USB3 and 2.4 overlap in frequencies).
All current LEDE release versions 17.01.[1/2/3/4/x] still seem to use the old mediatek Wifi driver (the one with the bug).
From my point of view, currently only the LEDE snapshot/trunk version has the bug-free newer mediatek driver version.
Just to point this out: The snapshot branch correlates to a next larger LEDE version (probably 18.0 or 17.2, but not to the next 17.01.x patch level).
Any current 17.01.x patch version is not created from the current snapshot, but from a backport of a small subset of that features.
E.g. the release versions of 17.01.x still use kernel 4.4, while the current snapshot version (while I am writing this) relies on kernel 4.9. I guess the developer want to give it some time, before releasing that, might be released as 17.02 or most probably more like LEDE version 18.0, but I don't know details about this. You may need to ask the core developers for further prelease planning of this.
I would not expect the 860L WiFi driver fix to appear in any 17.1.x release. For now you will have to stick to snapshot versions for that fix.
Any bugfix released as 17.1.x will also be contained in the daily snapshot version, but not the other way round.
Also note: The 860L relies on a Mediatek mt7621 (chip which is also used in devices of other vendors), the same bug may also appear on other devices as well that use Mediatek mt7621 in LEDE 17.01.x.
Try the snapshot in the meantime, it runs flawless, I am having no problems, you just have to manually add LuCi GUI installation.
Whenever a new 17.01.x patch version is released, just update to the most recent snapshot 1 day later, to keep up with important security fixes. Do this workaround until the next larger LEDE release version (probably 18) is released.
Good thing about running snapshots on the 860L is the 860L-built in recovery mode: firmware flashing effectively cannot kill it, making flashing a riskless operation on the 860L. So in worst case you will just have wasted some time.