Thank you for your answers.

Sorry that I forgot to mention my budget: it's around 100€.

if you look at Octagons web site you will see a bunch of usb wifi attachments, some of which show specs supporting 5GHz - so thats probably best solution, just make sure you download the appropriate driver from plugins if not installed.
So you might be able to use a cheaper receiver with a dongle…which Octagon also supply.
...at additional costs.
Perhaps I'm just on the wrong way to make a decision.

At the moment the SX988 with the 600MBit WiFi dongle seems to fit the bill very good - according to the specs.
There is only one very specific discussion about the SX988 in the forum yet. Which could mean that no one has any problems with the hardware.

Is there any other, better approach to choose the right product?
I'm just not sure...

E.