@Kaiperx 

Hi,

If the US driver is working fine for you, then just stick with it. It doesn't matter that much for a wireless client card.

What would be interesting to know is whether your wireless router uses two different SSID's (wireless network names) for the 2.4 GHz band and the 5 GHz band or if both bands share the same SSID. (on TP-Link routers that feature is called "Smart Connect", but other router manufacturers may call it differently)

By the way, could you please post the link to the V1.1 drivers here?

  @woozle Router both bands are in the same ssid. I was testing the speeds when adapter connected to 5ghz which happens after short while after being connected to the network.
I haven't found any V1.1 drivers. I just use V1&V2 drivers from here https://www.tp-link.com/pl/support/download/archer-t6e/

  @Kaiperx 

Ok, sorry, I misunderstood you about the V1.1 drivers.
I am pretty sure there is nothing different on the T6E V1.1 that would require dedicated drivers.

So, you are sure the T6E was indeed connected to the 5 GHz band when you got only 200 Mbps, right? 
Do you happen to remember what "Link speed (Receive/Transmit)" Windows showed at the time?

As for the two drivers you mentioned. While the timestamps of the files are similar the actual versions of the two drivers are different. The driver from the so-called "EU" package is version 6.30.223.228 and the driver from the so-called "US" package is version 7.35.317.1, which is basically a generation newer. Maybe the older driver did indeed have some problems that caused the speeds to be lower in certain scenarios.

Actually, there is an even newer driver version available on Microsoft Update for "PCI\VEN_14E4&DEV_43B1", which should be the device ID of the Archer T6E (you could verify this on your computer).

  @woozle Both us and eu drivers show 866/866 Mbps on 5Ghz network. so does the windows update driver that you showed that works just as well as us driver. It probably would install automatically through windows update but I have disabled drivers installation through it because it was messing with graphics drivers. Also yes I'm sure it with eu driver I was connected to 5Ghz. it was also losing connection and switch to 2,4Ghz often. overall it was acting really weird when using network with 2 bands in 1 ssid. disabling 2,4Ghz didn't help either and instead of switching to 2,4 it would just lose connection to internet while still being connected to the router.