300mbps N is applicable if you're running on the 5Ghz band. Which generaly you have to get a decent router to get. The homehub certainly won't support it.
It's perfectly possible to get 95% of the performance of Infinity over Wifi, you just have to be prepared to shell out for a better router. Get one that has dual radios, one for 5GHz and one for 2.4Ghz (otherwise your phones/other devices that don't support 5Ghz will drag it back down to 2.4Ghz anyway) and you'll be laughing.
I backup wirelessly over my 5Ghz N Wifi network and get 120 megabits/second up/down without an issue. (although I should mention that is being in the same room as the router I use, obviously it will degrade with distance).
In the end though, if you're not moving around that much, and you have decent power wiring, give the powerline adapters a shot. Or, use the power line adapters to have two APs at opposite ends of the house that both support 5Ghz/2.4Ghz and live in wireless heaven