I have a similar line of thought except I see the bottom end a little differently.
For me:
Lows 20 - 150/200Hz (I treat the lows all in one band and include sub bass as well as bass)
Lower Mids (which I also sometimes think of as upper lows) 200 - 500 Hz
Mids 500 - 2 kHz
Upper Mids 2 kHz - 6 kHz (but yes you can break this down into 2 bands as well 2K-4K and 4K-6K)
Highs 5-6 kHz and up
The lower mids is often an area where a mix can get clogged up a bit. Semetimes all it takes is a little dip around 250-300 Hz to clear things up nicely. The whole rest of the mix can sometimes change
(for the better usually) when you do this so try it first.
Harrison Mixbus has got a knob right on the master buss aimed right at this lower mid area and it works a treat. Just one small movement is all it takes.