I sent an email to Tamron today asking about the 7D Servo tracking issues. Here's the reply:
"We have not seen any tracking issues with the Canon 7D and this lens. Actually, we did our own testing here with the 7D and found that it worked properly. We also compared the lens with a Canon equivalent and didn't see any differences. Its true that some camera bodies track better than others but we didn't see issues with any bodies. Naturally, shooting birds at 600mm F6.3 is not an easy thing to do and I think some users may just not be used to shooting at this long focal length and F stop."
What's the latest from the CR group? This lens appeals to me, but I want to use it with my 6D and 7D.