Comment This is a non-problem. (Score 4, Insightful) 254
All the newer, faster equipment supports the 5GHz band. Use a dual-radio access point, and set aside the 5GHz band for n/ac only. Run legacy devices on 2.4GHz. Use different network names for 2.4 and 5GHz so that people put their newer stuff on 5GHz.
Easiest way to do this is have "networkname" and "networkname_fast". People whose devices support 5GHz will probably use the fast one. Those with only 2.4GHz-only devices won't even see the "fast" one and use the regular one. Everyone should be (relatively) happy.
5GHz has been a godsend for WiFi performance. Sure, it doesn't penetrate as far as 2.4GHz, but in managed setups this is wonderful. Spend a little bit more on additional access points and have MUCH better performance.