As I say here in the UK you can buy a 430iii (grey) for £215.00 and a 600ex-rt for £319.00 (£275.00ebay) thus not much in it, the ST-E3-RT is £189 (grey) so not worth getting now the 430iii is out (YN-E3-RT is £70.00), and I agree flash option + AF assist makes it much better option to pack a 430iii of the ST-E3. 600's do get heavy and if your packing 4 of them you know it. Saying all of that anything is what a person may need, IF I were lugging the 600 all day on camera you can bet those 100+g's may play on your mind, and shoulder haha..
Many say the 430iii's interface is much faster to use over the ST-E3 if that's your thing, I for one find the ST-E3's menu frustrating when you want to adjust power etc, same as I find it drives me crazy when I want to access the setting from the 5D3, why O why you have to keep selecting the sub menu is a PITA just to get to power!
I am not bashing the 430iii, I think its a feature packed speedlight, shame they missed out second curtain AGAIN or I'd scrap my ST-E3-RT+YN-E3-RT's
I hate missing features and workarounds