5Ghz range is less the 2.4, BUT there is way less congestion on the 5Ghz band and therefore you get faster transfer speeds.
I have my network equipment beside my tv (modem > router + switch). My office is on another floor so instead of running ethernet or getting the half-assed technology that a wireless repeater is, I went with a powerline network which I get 350mbps.
Repeater half assedness explained: if say you get a transfer rate of 100, a repeater will halve that because the antenna has to do both receive and transmitt. Adding additional repeaters piggy backed off each other halve your signal/speed for each one so you can end up with 25 trans rate by adding 2 repeaters.
A powerline (you can get a very good set for $60) works off your existing electrical wiring (as long has its on the same circuit break and not plugged into a powerbar). One adapter plugs into a power outlet with a ethernet cable. The 2 (or up to 7 usually) adapter plugs into another outlet and you run an ethernet from it. If you want slap a wireless router to it and you will extend your network better then using repeaters
Obviously hardwire is the way to go but for someone (like me) that didn't want to run 500+ ft of cable and having spend time patching holes, a powerline network is extremely viable (Belkin just released a 1gbps powerline adapter, but Zyxel makes the best ones according to my research). I'd also recommend getting a 500Mbps kit or higher (600Mbps by Zyxel is actually very good). The network is private, there is practically no configuration besides setting a network name and they sync automatically to each other.
Only way you'll increase you AC speed is by adding another antenna to your Air which isn't possible as the wireless card is 2x2 and not 3x3.
Using my Sager (3x3 Intel Centrino 6300 wireless) on 5Ghz I get 450mbps, about 15-25 feet away, more then that it drops.
Any questions just ask.
