In the USA most buildings are stucco, and drywall. 5Ghz works just fine. 5Ghz works poorly in Singapore. Buildings here are mostly made of masonry, and granite tile. The higher the frequency, the less range you get though dense building materials. Free WiFi is everywhere in Singapore, but not at 5Ghz.
Bluetooth and WiFi co-exist without problems on most computers, like Dell. Assuming the Bluetooth device is well designed, there is no problem. Typically the SMSC, Broadcom, or [insert maker here] combined Bluetooth and WiFi modules contain only volatile memory. The firmware is included in the kernel object, and is uploaded by the main CPU when the kernel object initializes. If the firmware is buggy, the chip will not perform well. Is the problem in the firware? I do not know for sure.
The performance is also very much dependent on how sloppy the Bluetooth device is. A cheap $20 (USA) iHome mouse or a fake "Beats" Bluetooth speaker can cause problems for a Dell, but not anything like it does on Macbook. I suspect cheap devices are using Chinese knockoff chipsets, and not the brand name parts.
If I use a cheap Bluetooth device near my MacBook my WiFi speed drops to about 100K per second. I can make the connection drop by moving the mouse back and forth quickly. If I switch the mouse off, my WiFi recovers.
After purchasing the Apple Bluetooth mouse ($89 Singapore dollars) the WiFi problem went away. The Apple mouse as better designed (and works very well, I might add).
Apple has a reputation for bad firmware on its devices. Remember back in 2008 they forgot to secure the built in web cam? That is why some nefarious coders were able to modify the camera firmware. They told the camera to ignore the "Standby" signal. That is why the camera could be switched on without driving the LED.
very annoying
