Our friends and colleagues at DPReview have performed real word tests with a Canon EOS 70D preproduction sample.
Note the great stability during focus (with particular attention to the video 3, 4 and 5 regarding the tracking test).
Imaging resource has made an similarly informative comparison between the EOS 70D vs D7100 vs Canon SL1.
In the video, the tracking mode behaves pretty well in comparison with the other models on test.
Another insightful (albeit unscientific) clip was performed by You Tube user marconilanna, which rather cleverly shows the different behavior between STM and USM lenses when used for video.
Petapixel produced an Canon EOS 70D overview based on marcolinna’s clip.
A review and tests performed by Optyczne