Average 5 GHz Downlink and Uplink Throughput charts both have the Asus RT-N56U in the lead, even besting other three-stream (450Mbps) routers. In the 40MHz bandwidth mode charts, it remains on top for uplink speed and is #2 for downlink, second to the Netgear WNDR4000.
The best price I can...
You need a pretty good signal to get 300Mbps. MAC filtering is not security as it can be spoofed easily.
Also, if your G devices are actively communicating with the router, it will reduce the speed of any N devices connected to the same radio since some N features have to be disabled in order...
Aren't the E2000's known for getting hot or was that just the E3000's? You might not want to set the router on that computer if the computer is letting any heat out the top up into the router.
Don't try to test your wireless network's speed by downloading from the internet, there are way too many potential bottlenecks. Transfer something locally.
Why do you say that your linksys router is dead? I ask this because I have helped a few people fix their router after they thought it was dead by simply resetting it and configuring it again.
Not all 802.11n devices support 5 GHz. No 802.11b/g devices support 5GHz. If you're using the built-in wireless on an XBox 360 slim, it only supports 2.4GHz.
You want to configure the router as an access point by disabling its DHCP server. Also, nothing should be plugged into the rotuer's WAN/Internet port, but into one of its LAN ports instead as serpretetsky said.
This is done on the Basic Setup page by switching the "DHCP Server" radio button...
Rosewill has never sold a PCIe WiFi card with three antennas so you probably have a PCI card. What is the model number of your card? If it's the RNX-N300X, go download the latest drivers from Ralink for the RT2860 and see if that helps.
Three antennas are pointless on a two-stream device...