I will take it a step further. I would say that with the introduction of the yn622c's, that the 600's are a waste of $$. You can use existing 580's and 430's in your kits and do the exact same thing that the 600's do for a heck of a lot less $$$.
Furthermore, if i were starting out, i would probably buy 430's and use them with the 622'c.......or the newer Yongnou versions of the 600's that canon sells.
Canon tried to force everyone to buy these 600's by discontinuing the 580ex11. This was a really bold move on canons part. There is nothing in their line up now except a 430 which is about a 3/4 stop less power output than the 580 ad 600's output.
I like having the ability to control A,B,C groups of flashes from back of the camera with canons systems but i dont like being forced to spend $500.00 for a flash. All canon had to do is do what Yongnuo did and make a trigger that would allow thier users to control the existing line up from the back of the camera.....everyone knows what canon did, everyone knows what yongnuo did.sales of the 622c have gone off the charts. Canon responded with a sale price on the 600's..........Pfffft. BFD.
Canon needs to wake up big time. Sigma is now putting out comparable lens for substantially less $$ and companies like Yongnuo are nipping at their heals on the other end of the market.
Ive been a very loyal canon client since 1974 but with their price structure i can no longer afford to ignore what is being offered by the 3rd party market.
my opinion is that the 600's are not worth the investment.