I shoot the very combo using my 7D, and 7D Mark II. When I started using the big Tamron, I had a problem with focus, and focus time. I kept checking my shutter speed, and I finally had to send in the lens to Tamron in New York, for calibration, and adjustment. I sent them sample images I got using the lens on my Mark II, to illustrate the focus problem. I also sent Tamron a list of my camera bodies, when the lens returned I got a very sharp lens. Tamron replaced several elements, and the focus motor, and calibrated the lens to my camera specs. The lens is again back to Tamron, for upgrade for the new 5D Mark IV, live view problem, and update of the VC. I've also learned not to place to much faith in the VC when the lens is zoomed out near 100%, you'll need that good tripod, and at least a good gimbal head. I use a Nest Gimbal, and a very sturdy Bogen 3011 tripod. You may also want to make some test images using your setup. Place a target a distance from where you set up your camera, and tripod. Really secure the camera and lens to the center of the target, and take several test shots to test for focus accuracy. Use both the viewfinder, and live view. In live view chimp the images and look at them with the zoom function. Be sure to use a remote shutter release, and mirror lock up when taking test shots, that is important. With a long lens, any vibration will effect the motion of the lens, and could cause fake focus movement.

B

I also had that same combination and was not happy with it. Similar to other people reporting with this combo, the longer I zoomed the lens, the more problems with sharpness I had. I MAed the lens numerous times with little to no improvement. I finally sold the lens and replaced it with a 100-400 II and a 1.4 TC III. Lot more money but also lots better results. With the 7DII you also give up some AF flexibility with the TC as you will be limited at F8 to just the center point. If I just use the 100-400 II without the TC though, I can crop my images to the equivalent of a 600 mm I retain AF flexibility and still get better images than with the Tamaron at 600 mm.