I have a similar set-up, ST-E2 which is great, but two light set-up doesn't work as well as I'd expected it to. It seems to under expose and I've not yet found a way to manualy adjust 2 flash units. I can manual adjust 1, but not with the transmitter. The transmitter has worked with the flash held above and behind me, so line of sight doesn't seem quite so crucial, but it was in a small room. I have 580 and 430 flash units for reference so similar to your proposed set-up.