"but I thought 802.11n was good only for upto 300Mbps"
No, not true... Belkin started with proprietary protocol and specific network adapter and router getting 450Mbps... now others have it as well.
Secondly, if you are going wireless numbers are numbers, no guarantee you'll even get anywhere NEAR it, especially when you go further away. For instance, N routers that are dual-band are the older 2.4Ghz and 5Ghz radio SSID. The 2.4Ghz is quite susceptible interference from microwave's, portable phones, other routers, etc. The 5Ghz isn't as much as 5Ghz router radio SSID are no where near as prevalent as the 2.4Ghz are and they operate on different bands. One drawback, the 5Ghz doesn't have as much of a range as the 2.4Ghz does.
On top of that, unless you are transferring files and/or running programs off of your local LAN computers, you'll never REACH the speed from the Internet. Yeah, some sites will match and use all your available Mbps, but most are just 'slow'.
If you look at the link Rick posted above this one, you'll see that router also supports 450N speed, but you NEED to have the companion Network Adapter to get it.