Ok.... I traced it down to when WIFI AC performance starts to get slower. I tested on my R710 with all other APs unplugged so things would be consistent. I started with unleashed firmware 200.2.x , but could not test it with speedflex since speedflex was not supported until 200.3.x.
Wifi speeds on 200.3.x firmware
on average
533.6 mbps down
779.3 mbps up
Wifi speed on 200.4.x firmware
569 mbps down
759 mbps up
Wifi speed on 200.5.x firmware
336 mbps down
615 mbps up
Note this was done on a Ipad pro 12.9 inch 2018 model which should have two antenna streams.
So starting with firmware 200.5.x and through 200.6.x wifi speeds dropped a bit from the 500ish mbps range down to the 300 mbps range...
I know the R510 on the 200.6. x firmware averages on the high 250mbps
Also I do believe th R500 and R600 is also affected. I do also have access the A R500 to test.... and as well as R510, and R610.
I do believe the firmware changes with 200.5.x impact the wifi speeds... and somehow this got made worse on firmware 200.7.x
This is really bad.. I can get faster speeds on a consumer 802.11ac router... starting with firmware 200.5.
Anyway one else wants to test my conclusions with firmware 200.4.x for those that have R510, R610, R710 and R310, R500, R600.?