So, at best you're using 40MHz channels which has effectively brought your max throughput down half again. If you're in a high-density (HD) environment like a Higher-Ed campus, or large event space, where you may have hundreds to thousands of APs, you're more than likely going to be using 20MHz channels, thus halving you throughput yet again. So, when you are designing for capacity you will be using smaller channels to increase that capacity at the expense of the maximum possible throughput of your shiny 802.11ac APs.
Lastly, those fancy-pants, "hyper-speeds" that are all the rage? Well, what they don't tell you in the marketing brochure is those speeds are only attainable when you are very close (less than 25-30ft) and have line-of-sight, with no obstructions, or interference, or other clients, on the AP. You need extremely high SNR (Signal-To-Noise-Ratio) to reach the unicorn-like 256-QAM that is required to get there. Reality is in most environments there are walls, desks, bookshelves, people, kitchens, and more, all between the client and the APs.
3. THE MAJORITY OF CLIENTS ARE NOT FULLY UTILIZING THEIR CONNECTIONS, OR THE CAPABILITIES OF THE AP.
Most wireless clients in enterprise, educational, or event environments are not streaming HD video, bittorrenting, or otherwise using as much bandwidth as they can. The majority are doing average things like web surfing, watching YouTube, e-mailing, accessing databases, Tweeting, Facebooking, Instagraming, listening to music, etc. - things that don't require extremely high, or even consistent bandwidth.
So, if you have 60-100 clients on an AP, many are likely just idley connected, and maybe a few are pushing serious bandwidth. If you look at statistics on your WLAN you will probably see that most users are not serious bandwidth hogs. Most likely your bandwidth bottleneck will happen on 1Gb uplinks between switches. This would be a good place to look to upgrade.
Also, there is wide disparity between clients. You may have a 3-Stream, 3-Radio, 802.11ac access point, but most smartphones are single-stream, or at best dual-stream. Even with laptops the MacBook Pro appears to be the only 3-Stream device on the market (for now). The fact is most devices (typically mobile devices) aren't even CAPABLE of matching the APs capabilities. So, those gigabit speeds you've been reading about? Ain't gonna happen.
Here's a good video that discusses client capabilities: