Thanks for the link and those before you for the reply.
A - B
A is archer c1200 at my sis house (with unifi)
B is Tenda AC 18 at my bro house (in universal repeater mode)
B is connected to A wirelessly.
About 4 to 5 devices at A
About 4 to 5 devices at B as well.
Before Tenda, it was tplink 1043nd doing the job. Max speed can get is only 17 to 20 Mbps (back then when A is unifi 30 to 50 to 100mbps).
Now with Tenda doing the job, it's 90 to 100mbps consistent (where unifi at A is now unifi 800mbps).
Coz of the good job Tenda is doing at B as repeater, we thought of changing A with Tenda AC 18 as well, even though if it might not fully support 800. My sis would still be fine if can get 300 to 500.
So that's my situation, and not sure if it helps you to gauge the performance on the Tenda under full load.
Should change c1200 with tenda AC18. I don't know why would you use c1200 as your main and AC18 as the repeater. AC18 is better than c1200, can refer 1st post and also from my experience, I've change from c1200 to AC18 and it is much better.