I have two 580s ad's I'm quite fond of them... And I have an opportunity to upgrade one of them for $50. It seems like a no brainer... would y'all agree...
Im using yongnuos at the moment to control my off camera flash... So only one 600 won't change that, but I suppose I may upgrade the other 580 eventually as well... thoughts?
Buy two 600s and sell your yongnuos if you can to fund the purchase. Then you won't wonder why you have one 600 whose rt function isn't of value until you buy another. As previously mentioned though, should you only get the one, you will find other benefits other than the rt function that can justify it. And as you say, you may buy another in the future and you'll be set.
I upgrade at a glacial pace. And even that feels too fast for me. I'm going to get the flash, but getting it past the wife will be a challenge.