its not dells only. I have read many posts online with other manufacturer's and if I buy a new 7260 card non oem ones then same problem occurs. this started with your 6 series and still lingering on. have you tried talking to the hardware team to isolate the interference. between the 2.4ghz section and 5 ghz section and Bluetooth section. in my brain it is logical that the chip has these three sections integrated and printed on one wafer. Any ways I have used this with 5 ghz dual routers connected to 5ghz ,,, it works fine at 5 and not at 2.4. so yes the problem is 2.4.
must disable u-apsd and disable Bluetooth to get stable speed.
main question to intel
is there a revision of 7260 chip which has more of these problems. how do we identify them and get them replaced from dell or Lenovo or whatever. this question is important for wellbeing of intels reputation. if they can honestly tell us then we can stop wasting out time having discussions here and doing the diagnostics for intel. we are not employees of intel.
I am sure you are having group discussion's time to time. Convey my message to all working on this project. (( You all guys are lazy to do the job right the first time around)).