Video quality can be better based on a lot of factors such as the lens you're using, ISO settings and ambient lighting conditions. The 550D (the 600D's predecessor) can take some superb quality videos and frankly, I can't imagine the A55 being appreciably better if you're talking about video quality and quality alone at their price point. In my view, the most noteworthy benefit the A55 has over the 600D in terms of video recording is that it has full-time AF so when tracking moving subjects, it can be much more convenient.
While the A55 can shoot faster, that doesn't always mean you'll capture the action better - there have been several reports of Sony's SLT cameras not focusing on quite the right spot in burst mode on the subject so the faster continuous shooting rate may become a moot selling point. That's not to say it doesn't happen with the 600D but you shouldn't rely on a dry list of statistics and specifications.
I don't know where you're based but any self-respecting CE/photography store in the Western world should allow you to try a camera since they should appreciate you're going to spend a substantial amount of money do you'd want to know you made the right choice. A chain store should have demonstration stock for your to handle. If a smaller store has no demo stock and refuses to let you hold and try the camera out, the chances are that there will be somewhere else close by more than willing to oblige you and you can remind them of that - if they won't open the box to let you try the camera out, neither should your wallet.
DSLRs: Canon EOS 7D Mark II, Canon EOS 70D
CSC: Canon EOS M3
Lenses: Canon EF-S 15-85mm f/3.5-5.6 IS USM, EF 50mm f/1.8 II, EF 100-400mm f/4.5-5.6L IS USM, Canon EF-M 18-55mm f/3.5-5.6 IS STM, Canon EF-M 22mm f/2.0 STM