Steve, I recently acquired a Tamron 02B 28mm so I dug up this comparison you did.
Thanks for dioing it, it made for an interesting read. On a different thread you asked about a M42 Vivitar 28/2.5 I also recently acquired, so today I had a bit of time and did a very brief, unscientific comparison of the 2 and for fun I threw in my Pentax-F 28mm.
With my K10D mounted on a tripod, and F-28 mounted, in AV mode and Sunny WB, I took 4 shots. 1 at f/2.8, 1 at f/4, 1 at f/5.6, and 1 at f/8. For each shot I recorded shutter speeds. Then I set the camera to M mode and took all 4 shots with each of the other 2 lenses and used the same shutter speeds as the shots from the F-28, I did adjust the shutter speeds for the 2.5/2.8 difference.
Not a great test but interesting to me. My Tamron seems darker than both the Pentax and the Vivitar. The Vivitar is cooler, and the Tamron seem quite a bit warmer than both.
Here is a link to the shots.
Picasa Web Albums - Colton - 28mm test
I hope you don't mind me posting this here.