I do ok with my 2 600 ex-rt's. I still need one more or a controller to have a complete setup. I hear complaints about canons current controller, so many people say use a 3rd 600 flash to control the others.
I love my 17-55, but don't want to have the second body (t4i) if I don't need it, that's why I was looking at the 24-70 II. The 24-105 is nice as hell, but sometimes I wish I had the 2.8 over the 4. Especially when shooting indoor events. You can check out my work here: www.facebook.com/AFlashInTimePhotographyByDonPedro
Most of the shoots before Oct were with a t2i and t4i. The newest stuff was with the 5DM3.
I would love a 24-70, but some would argue I don't need it.