Configuration for dual-band WLAN?

Question

I have an X230T with Intel N-6205 and 2x2 antennas.  AFAIK it is capable of parallel WLAN connection on both the 2.4 & 5 GHz for maximum bandwidth. How should I configure my WLAN to take advantage of this.  Should both 2.4 and 5 GHz networks have the same SSID?
X320T running Windows 8 Pro x64

Answer 1

Actually, those settings I provided you are from my Intel Dual Band Wireless-N 7260 adapter so some settings are a bit different, but it should work for all Intel Wi-Fi cards.
rsbrux wrote: 
"I also have a secondary router, whose 2.4GHz radio I had set to 20 MHz BW, as there are more other 2.4 GHz WLANs near it.  ISTR reading that the narrower BW can actually yield improved throughput under such conditions, and the secondary router has no "auto" BW option.  What do you think of this?"
P.S. If I understand "NS offload for WoWLAN" correctly, it seems to be enabled.
At least, the WLAN adapter appears to turn itself on, even with the laptop powered down and connected to a wired ethernet.
As billbolton pointed out, he is 100% correct that "The 2.4GHz WiFi band has become so congested with competing traffic in many densely populated locations that useful 300Mpbs connections are quite unlikely to be achieved."
Based on many networking articles, 300 Mbps is achieved through channel bonding (40 MHz) on both bands. Since channel bonding makes the channels wider, this would actually result to more overlapping with other channels from routers nearby on the 2.4. Channel overlapping should be avoided since it induces more interference thus making your ping spike often as well as frequent reduced throughput and link speed. On the worst case, you will experiece dropped connections. If you absolutely have to work on the 2.4 GHz band with a lot of neighors, you can leave the Wi-Fi adapter settings I provided to be the same, but you have to change the channel width on the router to 20 Mhz only for 2.4 GHz band and leave the 40 MHz channel width on the 5 GHz band. This would cut the speed to 156 / 150 / 144 Mbps on 2.4 GHz band only, but you only occupy 2 adjacent channels from the channel you're broadcasting instead of taking over more than half of available channels using 40 MHz. Like many networking articles online, 40 MHz is ideal for 5 GHz since very few people use that band and there are far more available channels to choose for the 5 GHz without overlapping with other channels nearby.
As for your PS note, the reason the WLAN adapter is awake while the computer is asleep is due to Intel Smart Connect Technology: http://www.intel.com/content/www/us/en/architecture-and-technology/smart-connect-technology.html
Lenovo Y470: i7-2670QM | 8 GB DDR3 1333 MHz RAM | Nvidia GeForce GT 550M | 500 GB 7200 RPM Seagate HDD | ASUS PCE-AC56 802.11ac Network Adapter | Windows 7 Professional 64-bit