Macbook Pro Wifi @ 108mbps, iPad/iPhone @ 18mbps. Why?
Experiment with the prior post.
Then Step 2.
Give your 5ghz network a different name. Home-N vs Home-N5. So that when you connect to the network Home-N5 you definitely know you are on the 5ghz band.
Do that with your idevices.
IPad air should be able to hit 100mbps speedtest.
IPhone 5/5S will top around 75.
Experiment awhile, if no success, report back, I have one more thought.
Ive personally had stability issues running the SSID split with mine, so. I keep it combined, even with the speed hit if they authenticate on the 2.4ghz, its not a big deal.