I recently installed the latest 21.02.3 firmware on my WRT1900AC with V1 hardware (mamba).
Performance is nothing short of stunning! Really good. I get bitrates in excess of 600M on the 5GHZ radio and my full cable modem speed almost anywhere in the house.
I also own a WRT1900ACS - Hardware V2. I tried 21.02.3 on that and results were not so good.
Bit rates on 5GHZ only about 160M. I also notice that the Radio order is swapped around in the GUI wireless view (Radio 0 is the 5GHZ one, Radio 1 is the 2.4GHZ one) compared with the 1900 AC. I can get the ACS router to work but It's not as fast as the AC and that is inferior hardware (slower CPU, less RAM). Stock ACS Linksys firmware outperforms OpenWRT which is not the case for the AC.
I notice there is only one version of Open WRT for both hardware versions of the ACS. Is this correct? There are individual versions for V1 and V2 of the AC.
Are there any parameters I could change?
I know I have pretty old hardware but my WRT1900AC with OpenWRT outperforms stock Linksys firmware, My WRT1900ACS and Netgear R8000P Nighthawk. SERIOUS KUDOS TO THE WRITER!!