I am wondering if budget is driving you along this route.
I have 4x 600 Ex Rts all triggered by the STE 3 .
I did have 2 of the 430 optical flashes before , I would never ever go back to that optical route.
However I did have 2x cheap Yongnuos spare , these have an optical cell on them and they are a great budget way of getting additional fire power cheaply.
Shooting a model in woodlands. Basicslly 2x 600s fill flash the head and bust, the other 2x 600s do from the waist to feet.
If say I want some of the woodland background illuminated, these are set manually and are set to the internal optical cell triggers. So the 600s do all the clever ettl2 fill flash stuff on the model and the 2x yongnuos (£40 each ) illuminate the background woodland. They fire every time, just a bit of a pain manually setting them to output the right light level, but one gets pretty good at guessing the power level.
The main thing is they cost £80 for 2, and the same power in 600s would have cost me £850!
And the nice thing is the model will be illuminated perfectly, well accurately, by The 600s .
Canon EOS 5DS R, Canon EF 70-200 F2.8 L Mk II IS USM, Canon EF 70-300 F4-5.6 L IS USM, EF 40mm F2.8 STM , RC6 Remote. Canon STE-3 Radio Flash Controller, Canon 600 EX RT x4 , YN 560 MkII x2 ; Bowens GM500PRO x4 , Bowens Remote Control. Bowens Pulsar TX, RX Radio Transmitter and Reciever Cards. Bowens Constant 530 Streamlights 600w x 4 Sold EOS 5D Mk III, 7D, EF 50mm F1.8, 430 EX Mk II, Bowens GM500Rs x4