No, I have never used QoS because in my experience, ever since my first high speed connection (1mbps back in the early days of Blueyonder) i have found QoS generally slowed stuff down. Technology might have moved on but i have never found a need for it.
I do have some good news though, i have re-enabled wifi on the D7000 but disabled 20/40 MHz co-existence and so far it has been up for a couple hours and not crashed yet...
Agreed it shouldn't crash based on a settings but we all know from experience that environment can play havoc with wifi networks. I live in a block of 9 flats and there are at least 5 other SSIDs broadcasting, god only knows how many of those are dual band. Then there is the fact I have Sky Q which is broadcasting its own (separately named) dual band SSIDs which i cant turn off.
Add into the mix an unknown number of wireless devices in what is a fairly confined space and its easy to see there is a lot that could possibly impact on a Wireless router.
Sure my previous router, HH5 and apple airport never suffered from the problem but crucially none of those devices have the same co-existence setting