Developing Tri-X at 800

I wanted to use Tri-X 400 at ISO 800. Kodak says to develop at 800 the same times as 400 and only push process (extend developing times) if shot at 1600. This doesn't really make sense to me. Certainly there is some benefit to extending developing times a little bit. For 70F, D76 1:1, at ISO 400 its 9 minutes and ISO 1600, it could be a guessing game what the proper developing time should be without guidance from Kodak. Is the average appropriate?

I decided to graph the known developing times (400,1600,3200) and find the closest regression. Then I could find ISO 800 on the curve. I believe exposure and developing is really a log based scale, but Kodak rounds its developing times to the nearest quarter-minute. So for D76 1:1, I was getting better results (r squared values) with a power curve.

The results:

D76 stock 68F: 8 minutes 8 seconds
D76 stock 70F: 7 minutes 28 seconds

D76 1:1 68F: 11 minutes 25 seconds (11'38" with a log curve)
D76 1:1 70F: 10 minutes 38 seconds (10'45" with a log curve)

The charts:





How does it compare:

A pure average of the 400 and 800 times would give a slight increase in developing times of 5-10 seconds.