A lot depends on the client as well but on the AX1800 as it’s a 2x2 and your clients are probably 2x2 at the max rate QAM being close to the router you are roughly in the ball park on a 5Ghz 80Mhz setting.
The max I’ve seen here on a typical AX1800 router is 856mbps on an iPad Pro with WiFi 6 but you will find on the NG 1800 router your throughput drops as you gain distance. If you step up to the RAX120 which has better hardware the throughput is greater over distances but you don’t gain extra throughput on a 2x2 client.
As you’ve noted clients do make a difference. At the moment I’m running a UDM and have 2 iPad Pro’s. Ones the 2019 pro and ones the 2021 version and running on a WiFi 5 router on 80Mhz on 5Ghz I see 100mbps difference in some rooms between the two of them with the 2021 hitting a respectable 640mbps at close range.
