Popped into a camera store today, to look at the 70-300L IS USM ($1549) and the Tamron 70-300 VC Di ($449).
There's now no point in buying the 70-300IS USM (non-L).
Ok, so I agree with your thread title about the Canon 70-300mm IS (non-L). Looking at a comparison of those two lenses at 70mm f/4 and at 300mm f/5.6, the Tamron is better (although neither is good at 300mm).
But, you are really talking about 3 (4 counting the Sigma) different 70-300mm lenses here, and you also seem to be saying that buying the new 70-300mm f/4-5.6L IS lens is pointless. Or do I misinterpret the '$1100 for white paint' comment? (Oh, and you forgot to mention weather sealing.)
When TDP compares the Tamron 70-300mm to the new Canon L zoom, at 70mm f/4 the Tamron is a bit sharper across the frame (surprising, but the Tamron is reportedly a very sharp lens. But, at 300mm f/5.6 (which is where you took your test shots) the Tamron lens looks, well, like crap, and the Canon is still quite sharp.
So, are you saying that in your hands, the Tamron performed as well as the new Canon 70-300 L, or just better than the old Canon 70-300 non-L, or both? If it's the latter, maybe you can show some 100% crops to back that up? I know Bryan at TDP has a careful setup and from his testing, as you can see in the links above, the Canon L zoom is fairly similar to the Tamron at the wide end of the range (kudos to Tamron), but the Canon L is clearly better than the Tamron 70-300mm starting from 135mm onwards (which seems to result from degradation in the Tamron's performance as you zoom in, while the Canon stays sharp).