It would have to be my 400mm 2.8 mkii and 135mm L
I wish instead of bringing out new flashguns they would bring out a receiver unit for the ST-E3-RT to make the 580's compatible...
That would be an ST-E2!
I really don't understand the dissatisfaction here, Canon did a very good job of making the new flash compatible with 100% functionality of the legacy gear going all the way back to the first EX's. They didn't have to include optical triggering reverse compatibility, it wouldn't have altered my decision to buy three 600's and an ST-E3-RT and having used them for a few weeks I know I will be buying more, but give credit where it is due, Canon did include it. You can buy one 600EX-RT and if you already own older EX Speedlites or a camera with a commander built in you are good to go.
The ST-E3-RT has only a radio transmitter. The 580 has only an optical receiver. The 600 has optical and radio transmission and reception.
An ST-E2 could trigger both the 580s and the 600, optically.