The 600EX-RT is an awesome unit and provides everything the 580 Speedlites do plus the benefit of radio control. The 600EX-RT also includes a couple of gels and gel holder to mount over the flash head. I still prefer using Honl gels so this is not a influencing factor for me. The freedom of radio control was my motivation for switching.
I used to have a 580EX II and a couple of 430EX IIs. I sold them and now have a couple of 600s and the new transmitter ST-E3-RT. I could not be happier with this setup. The 600EX-RT and ST-E3-RT have the same new and improved control panel.
The 600EX-RT still has optical functionality like the 580 and 430 units so the 7D can trigger the 600EX-RT as a slave unit (the 7D being the master of course). If you just need a simple on camera flash that has more power and coverage than the7D's pop-up flash, the 600 might be an over-kill. You might look at the (now discontinued) 580EX II or even the less powerful 430EX II. However, you plan to get into OCF (off camera flash), and multiple flash units then I would look at the 600EX-RT.
In order to take advantage of radio control (with OCF), you will need either a second 600 or the ST-E3-RT. One 600 be setup as a slave, and the other 600 or ST-E3 will be setup as the master.
Keep in mind with pre 2012 cameras like the 7D, you will not be able to use HSS (high speed sync). Read this excellent article here about using pre 2012 cameras with the 600EX-RT.
If HSS is not an issue, and you want to use radio controlled OCF then I would definitely go with with 600. If you are planning to get a new body someday or use multiple flash units, the 600 is the way to go. Expect a smaller radio control Speedlite to be available this year to replace the 430EX II (it has been rumored for several months now). The 600EX-RT replaced the 580EX II last year.
So you will need to determine your current and future needs and build a system to accommodate that. You will find many other shooters recommend 3rd party flash units and Pocket Wizards to control their Speedlites. If you have the budget and the 600EX-RT suits your needs, that is the way I would go.
Download the 600EX-RT pdf manual here. Some additional reading here:
Me too. Sold my 580EX II, 580 EX, Metz mecablitz 58 AF2, Yongnuo 560 and cybersync transmitters. Picked up an ST-E3-RT and two 600's. Gonna get a third one soon. I do not miss triggers and cables.
Very good explanation from 7D5D. I just want to add I think the menu system is much improved and the display will illuminate when you press any button. You can program it to stay on. Easy access to switch from master to slave and the control group mode is excellent. I carry the ST-E3 around and fire the flashes with the test button. I can shut off the other flashes while setting another up.
I cut up an old mini stand, attached a spare Black Rapid connector and clip it to my belt. I hold my Sekonic LM in my hand. When done I connect it to the hotshoe. Only con is there is no AF focsus assist.
You might find my post I wrote last year about using the Speedlite 600EX-RT on older cmaeras like your EOS 7D helps...
Brian / p4pictures