What LAN speed over wifi should I expect on RA-AC88U?

[Mastiff]

I have set up a new AIMesh system at home, and I had very slow speed over wifi, below 5 MB/s on transfering large files from the server (the main router in the AIMesh is in AP mode, my Windows Server 2016 Data Center Edition takes care of the connection). I found a post @doczenith1 about disabling stuff:
2.4gHz:
Turbo QAM - Disable (Only helps with clients that support it and there are not very many)
Airtime Fairness - Disable
Multi-User MIMO - Disable
Explicit Beamforming - Disable
Universal Beamforming - Disable

5 gHz:
Airtime Fairness - Disable
Multi-User MIMO - Disable
Universal Beamforming - Disable

I was unable to find the Turbo QAM, though, maybe that's not a part of the later ROM's? I have the very latest Merlin, and it was set up from the ground, no settings backup since they were band new routers and I have not had 88's before. Anyway, that made speed go up to about 18 MB/S. I can live with that, but it's about half the speed I had before, with an AriTies-setup. The range is better, though. I have cabled backhaul to the node, and the speed seems to be the same on the main AP and the node. But shouldn't it really be a bit faster?

 

[L&LD]

Is the router really an RT-AC88U instead of an RA...?

Between what two devices are you transferring from to see these speeds? Does testing between to wired clients give the expected results?

What files (sizes and file types) are you using for your testing?

Do you have Smart Connect enabled?

What models are the other nodes?

 

[Mastiff]

Sorry, my mistake. Of course RT-AC88U. I have tried two different computers, one of them is my Surface 6. On wired (through the switch on the Asus main router in the AI Mesh) I get around 105-106, but wireless only gives me around 18, but very stable. I have been testing with the type of files I always use, because that's what I need to transfer: AVI files, in MJPEG coding. Smart Connect is not enabled, and both nodes are the same RT-AC88U. I bought two used for a pretty good price to set up this because the range of each of them, with the antennas, should be better than the range of any regular mesh router without external antennas, like the D9 or the Omni.

 

[L&LD]

Surface 6? Can you try with a PC that has Intel NIC's instead?

 

[Mastiff]

I finally managed to find an old Dell with a 6220 NIC in my "museum" of old laptops. And that clocked in at 60 mb/S! Weird thing is that I tested the Surface again after that, and now it suddenly manages around 40. I have no idea what's happened, because I didn't change anything... Almost as the AI part in the AIMesh needed some days to adjust. Which is of course total bull, so something must have changed. I just didn't do it conciously.