I just made a spreadsheet to calculate the percentage of F seats in CO's and NWA's domestic fleets (multiply each aircraft's seat count by the number of aircraft in the fleet). Yes, I have too much time on my hands. When I get more I'll add DL's fleet.

I assumed all CO 738s and 739s had the extra 2 seats, as I have no idea of how many have been done. I put the 752s in COs domestic fleet, but did not include NWA's WBC 752s. This results in a trivial improvement and decline in CO's and NWA's averages, respectively.

Including all express/connection/airlink aircraft, we get:

CO: 7.4% of domestic seats are F
NW: 10.2% of domestic seats are F

Does anyone have a count of upgraded 738's (16 and 20 F seats, instead of 14 and 18) and 739s?

Also, what's CO Express's current fleet? I am using:
E135: 30
E145: 175
CRJ-200: 25

For CO Connection I have:
Q200: 15
Q400: 3
S340: 42
1900D: 26

I did not include CO's 767s or 777s. The few domestic flights they do (2 weekly for the 777?) mean they don't really matter. For NWA I didn't include the A330, 747, or WBC 757s (16 of 55, right?).