Don't forget though, Wireless N is still in it's "draft" stage, where they can change anything at any time. The improvments of Wireless N over Wireless G is the Range it can get (certainly a lot farter than my Linksys WRT54GX will possibly ever be able to transmit) and of course the speed (hearing 300Mbps roughly). Not to mention, N does use the less cluttered 5.2(?)Ghz range and can do 2.4GHz, so there's more channels for you to use as well which means more speed and less dead zones being caused by neighboring routers. Yeah, the routers may be expensive, but if you torture it enough by shoving high bandwidth apps and huge internet pipes at them, along with Torrents and Steam, they can do wonders (because of their CPU power, RAM for NAT, and the WAN to LAN/WLAN throughput they are capable of handling). Take Verizon FiOS for example. That is a consumer (and business) grade fiber optic product, where unless you have one of the speeds lower than 20Mbps/20Mbps, you won't find any cheap router that will be able to handle the throughput. Their top speed is 50Mbps/20Mbps, and already they're toying with 100Mbps and even 200Mbps speeds on the download. Now that NEEDS a big router or a PC with Linux to do the work. Unless of course you want to buy a very expensive Cisco
Your speed fluctuations might be being caused by Wireless G/B devices connecting. When this happens, since those cards cannot do 300Mbps rates, the router compensates for that by slowing down the overall wireless speed. Newer Wireless N routers, however, come with two or more radios. One radio is for Wireless N exclusively, while the other radio is there to support Wireless G/B devices without slowing down the N band.