What is the advertised bandwidth of your "high speed extreme" internet? Unless it's over 10Mb, and actually delivers that, then even a g wireless network, or 10Mb wired connection, can handle it.
In other words, your LAN (and router) is probably never going to be a bottleneck.
I had a computer with an N wireless PCI card connected to an N router. I have FIOS internet at 15mbps. I switched to a hard wired 100mbps connection and the hardwired connection was noticeably better when surfing the internet. In theory, a G connection should work as well as wired and a N should work even better than wired, but in practice, I've found a wired connection is always better. I think a steady reliable 100mbps is much faster than a signal that can go up to 300mbps, but goes up and down like a yo-yo.