I was experiencing wifi disconnects when I would toggle on bluetooth, when using CM11 M10 or higher.
With a clean install of Cm11 M12 (reset/new user + formatted /system), I finally worked up the courage (and kinda' understand what it is I have done) and updated the bootloader (not sure if necessary) and the GSM/LTE modems to the latest - XXUGNK4 - from here http://goo.gl/RziHz1
I was previously on XXUFNC6 (from the stock ROM), went to XXUGNI2 (closest to my country based on this thread http://goo.gl/TQi3gz) but that did not work either. So I went straight for the jugular, and installed first the bootloader, then the dual modem pack for XXUGNK4.
So far testing has yielded positive results.
Streaming audio (320mbps) via BT plus downloading some ISOs from MS (speed between 550KB/s to 1.01MB/s), and so far no issues.
Not saying this is going to work for anyone else, or solve the OP's exact issue, but it seems to for me.