When using a dual band router you can choose to use the 2.4GHz band for old 802.11G devices only and the 5GHz band to wireless N devices.
In your case since one computer have the Intel® Centrino® Advanced-N 6200 and the other the Intel® Centrino® Advanced-N 6230 you can setup the adapters to use the Wireless-N connection with the 5GHz band and it that way use the band that has less interference to get the higher speeds.
One good thing is to have the latest version for the Intel drivers, for both computers the latest version is the 15.1.0
The latest version for Windows* 7 are available at:
Intel® PROSet/Wireless Software and Drivers for Windows 7*
Other good option is to verify the settings of the wireless cards, there are some very good articles in the Intel website that you should check:
How do I improve my 802.11n wireless performance?
What are the recommended settings for 802.11n connectivity?
Why am I not able to connect at 300Mbps with my 802.11n device?