Hi Frank
With 802.11ac being a 5Ghz only standard, you might have to look at your AP deployment/location.
With 802.11n alot of wireless networks was designed around 2.4Ghz, this now will need to change to be designed around 5Ghz
You will need to ask yourself what is your client/application requirement?
Do you require the AC speed.
To obtain speeds close to the advertised AC speeds you have to use 80mhz channels.
This is not pratical in a densely AP populated area.
In dense areas you will have to look at channel reuse and for this you will have to use 20mhz channels but might look at 40mhz channels.
So to summarize the optimized settings to obtain the best speeds will differ from site to site.
It all depends on your client/application requirements.
Regards
Andre