The Tamron is not as good as my Canon lens. For extreme crops under poor conditions I use the Canon. However, the Tamron is good enough for most of the time. Here is a selection i took with the Tamron, going down the page at 309mm, 450mm, 600mm and 600mm. They might not be up to your standards, but they are good enough for me.
ps - they are all 100% crops. The EXIFS are on the images and you can download to read.
Thanks for sharing, Alan. Yeah, the 309mm shot is fine for me. The 450mm is not a disaster, but the 600mm for me would be unacceptable, and looks similar to what I got with the 300 f/4 IS + 2x TC: washed out color, low definition. Reminds me of a bunch of shots I had to toss from a wildlife safari trip with that combo, where everything with IS or a TC went in the trash bin.
You obviously have high standards. The emerald dove was taken in terrible light, f/6.3, where the lens is at its weakest, iso1250, which is higher than I like to go, and 1/250 s, hand held. Here are a couple of better examples. The mandarin duck was a f/6.3 again, but iso640 and 1/1250 s. The wigeon was at f/8, iso640 and 1/1000. Both at 600mm and hand held.