Thanks Tim!
If wireless range is not good (SNB's router ranker shows the WRT-1900AC as 4th in range in the AC1900 class), I may return both of my WRT-1900AC (unopened) and stick with the two AC66U units (#1 for wireless range in the AC1750 class).
Perhaps firmware updates will help the WRT-1900AC, but I may just return them for now while I am within the return period.
I am disappointed to see those results after the limited feedback from users seemed very positive (so far), but will wait for the write-up (review) details before passing full judgment...
It is interesting that others (admittedly based on limited user feedback at this time) seem to be having slightly better results than the higher ranked routers (R7000 e.g.)
Tweaktown review got better results on LAN and WLAN. Its a tie with R700 and tad better in other areas.
And you can open the routers and return them with in 15 days. It is a must for you to test the routers on your own, in your own environment with your own hardware.