First at all you should know that this lens need light ... a lot of light, but depend what your body will produce at high ISO, you might have some good surprise when light is starting to lack
The colors produced by this lens are good, really good IMO, even surprisingly good.
The contrast is also excellent, may be a bit too much, may be ... i said that because i think Tamron made this lens with a well contrasted projected image to compensate to make the picture look like more sharp that it is in reality
Sharpness ... that it's not bad at all, seriously in sunny day it can deliver nice details, and can be surprisingly good, may be comparable to the 100-400 !
Autofocus > in noway the AF system is good as the 100-400L (and it's not the fastest from Canon), but Tamron is not bad at all, a bit slow compare to the 100-400L, but accurate and work well also in AI Servo!
i should say i missed few times some birds, in 1 month of testing, that i would never miss with the 100-400L, due to the AF "searching" to being late to "lock".
There is a switch on the side of the lens to make the AF faster by reducing the length the AF need to move when you put the lens from 15metres to ∞, and it really goes faster.
But ... 15metres to ∞ ... seriously ? in my case it's totally unusable, 15 metres it's already too far when birds are 10 to 15 cm small > Tamron what are you thinking ? i would prefer a less "fast" option by limiting the AF from 8 or even 10 metres, but 15 metres ...
Image Stabilization (Tamron call it VC for Vibration Control) is efficient and very quiet, i cannot really say which of the Canon or Tamron is better, but i might give the advantage here to Tamron (i feel it is better than Canon, but didn't really check), there is no IS / VC mode, like mode 2 for panning on Canon lens, i didn't tried to pan with it, i'll will update it when i will do it ( i mean with > a slow shutter speed, there is nothing to write about it if i am at 1/1000s or more )
So for me this lens is a kind of compromise, i tested it for +1 month, and few days ago i decided to buy it in replacement of the 100-400L.
Compromise why ?
Sharpness, on the edge of the picture, i down grade a little bit (but it's the edge, so it's ok for me)
AF, i down grade a little bit.
Focal length, a huge upgrade in my case, with the 100-400 i was always too short, i shot birds mostly with a 7D and less often with a 5D3, i bought a Canon TC x2 III but on the 100-400 it become a piece of crap and the picture are unusable at ALL !
Tamron 150-600 produce good picture on both 7D and 5D3, the colors are rich, excellent contrast, quite good sharpness over all, in sunny day it get even better and i got birds which was too far with the 100-400 and i fulfill the frame were before i needed to crop it !
Calculation is simple on a crop sensor like the 7D.
400mm * 1.6 = 640
600mm * 1.6 = 960
Almost 1000mm equivalent FOV on the 7D compare to the +600mm before with the 100-400 and on the FF i got the same FOV than before with the 100-400 on the 7D ... the compromise win for me!
You want to see some pictures ?