The 867Mbps ones are likely to support 2 spatial streams (via 2 antenna) of 433Mbps each, using 80MHz of spectrum (ie 4 consecutive channels). The 433Mbps ones are likely to support a single stream using 80MHz.

You'll only see more speed from the 867Mbps dongles if the AP or router also supports multiple spatial streams.

Exactly how much speed will depend on the spectrum used - 20, 40 or 80MHz.

A bit more info here:
http://apcmag.com/five-things-to-know-about-80211ac....

If you want to understand a bit more about the 5GHz channels, especially if you want to use some of the ones above the standard 36-48., take a look here...
http://wifinigel.blogspot.co.uk/2015/01/5ghz-in-uk-w...

Get a wireless AC card. I would say go for the best you can get, my macbook supports 867 I believe, could be higher.

Will the HG635 support it ok ?

In reply to a post by stevenfrenchy:

Will the HG635 support it ok ?

Yes the HG635 is also the same wireless spec