Is it worth upgrading from 802.11n to 802.11ac if you are going to stick with 20 Mhz channels?

There are many Wi-Fi networks around our office, so we can't use 40 Mhz channels in the 5 Ghz spectrum.

Would it be worth it to upgrade to 802.11ac from 802.11n? We are using a Cisco Wireless LAN Controller and have 4 lightweight access points all running 20 Mhz channels in the 5 Ghz spectrum.

These APs are installed on two separate floors (we have two suites) in an office park that are right above / below each other.

There's an additional radio module that can be installed in the access points to give them 802.11ac functionality, so I was wondering if it would be worth it and possibly give us extra throughput. We stream a lot of video and there is a lot of VoIP traffic that runs on our wireless network.

This is a repost of an earlier question that was removed by an admin. I've been asked to repost it with additional information.