I have an Archer C 1200. My Internet speed to my house is 100MB. With the C 1200 5.4G radio I measure the speed as 100MB using OOKLA speed test.

However, with the 2.4G radio, the speed test result comes in under 40MB and most typically at about 35MB.

I don't know why I have such a difference in speed between the two bands. The Archer C 1200 is supposed to do 300MB at the 2.4G band, so 100MB should be easy for it. Yet it rarely gets to 40MB.

I have tested it while sitting next to the C 1200 and also from downstairs. I get the same performance from both bands in either place (<40 MB for 2.4G and 100 MB for 5G). 

I've thought about upgrading to a better TP-Link router, but don't want to if I can expect the same downgraded performance from the 2.4G band on a new TP-Link router.

I use the 2.4G band because some of the other devices in my home (TV and some home  automation devices for example) only operate at 2.4G (won't operate at 5G), and I don't want to have to switch bands back and forth depending upon what devices I am communicating with.

What should I do - look for another router besides TP-Link? Why am I getting such a performance difference betweent he 2 bands?