My BQ chances

What type of condition is required for a BQ? I'll base that off my 10K/5K ratio and extrapolate it to Full/Half. According to McMillan, a 40:00 10K calculates to a 19:15 5K for a ratio of (40/19.25)= 2.077. Again, IMO, that's too aggressive. Self-coached runner's ratio is (40/19.0)= 2.105. My current ratio is approx. (41.5/19.5)= 2.128 (I'll round it to 2.13). Of course, that could change come November when I race a flat 10K in Mobile. Also, if I can manage to run 60 MPW on a consistent basis, that ratio will come down a bit. Maybe, it could go as low as 2.10.
Now, let's try to extrapolate it to FM/HM.
Given my current ratio, my half marathon must be at least (191/2.13)= 1:29:40
Using Self-Coached runner: (191/2.105)= 1:30:45
To make it realistic and taking into account the wall, let's add another 10 seconds/mile to the marathon pace. That puts me at about 1:27:30 based on my current ratio and about 1:28:30 based on Self-Coached runner.
Here's my probability breakdown:
Sub-1:25- Slam dunk. Barring disaster, it's mine
1:25-1:27:30- Good shot, no guarantee but I like my chances
1:27:30-1:28:30- slightly better than 50/50, It could come down to the last .2
1:28:30-1:29:40- Would need an unusually good performance on race day.
1:29:40-1:30:40- Need a minor miracle on race day or sudden improvement in fitness.
over 1:30:40- no hope, just shoot for 3:20.
Figure that I need to be somewhere between Level 5 and Level 6 fitness for a 3:10 (refer to my last post). For a 3:15, all I need is to be slightly above Level 4 and I am nearly there now.
The key will be consistent mileage. I tried to run 60 MPW over the winter and got hurt but at that time, I wasn't healthy and had been wearing improper orthotics. I don't deny that the odds are long but my chances were zero in my last 2 marathons. This will be the first time I enter a training cycle with any chance at all and I am getting excited.