I said that I was able to use 2.4GHz reliably despite it being crowded. I only switched to 5GHz because I noticed no one was using it and I saw higher bandwidth on it from 5GHz 802.11ac supporting higher channel widths than 2.4GHz 802.11n supports.
In fairness, I had made tweaks to iwlwifi's kernel module options in order to have usable wifi on my laptop. Until a year ago, I was accustomed to have a hellish experience in congested areas until I turned off Bluetooth coexistence support in the iwlwifi driver. That feature would almost always cause severe packet loss on my T520 in crowded environments even when there did not appear to be any Bluetooth traffic.
Anyway, it is possible to get wifi working well for certain workloads in crowded environments. Making it work well in general might require better drivers and better equipment than one might have at first though. For example, I understand that ath9k was a disaster when it was first made, but it is fairly decent now. I ran an AP off an ath9k USB wifi dongle in China at one point and it worked well too. I doubt that would have worked as well with drivers from 5 years ago.
Also, from what I understand, a used Ruckus Zoneflex 7982 off eBay ought to be able to handle just about any environment fairly well. Their proprietary beam forming hardware is special because it attenuates signals coming from other directions than that of the client. The only exception from what I have read is when other wifi equipment is right next to it (e.g. practically touching). Some review of it said that it failed to work until they moved other equipment away after consulting Ruckus. I cannot find a link to it though.
I placed an order with an eBay merchant that I expect to receive soon. $90 per used Zoneflex 7982 (that had a $1099 MSRP when new) is a bargain considering that these still provide some of the best wifi in the world. There are reports of these getting good throughout through multiple concrete walls:
http://www.cio.com/article/2388827/wireless-networking/revie...
A newer version of the midrange model in their product line (that has inferior radio specifications to the top end model) was able to give a cell phone decent throughput from 225 yards away when the (omnidirectional) AP was in doors:
http://www.evdoinfo.com/content/view/5077/64/
As far as I know, the only better access points are the newer Ruckus models that replaced it. I am really excited to be getting one later this week. :)