I also bought one 600 EX RT and really like the flash, but instead of buying the ST-E3 I bought the Pixel Kings instead, but am thinking of also buying the ST-E3, doesn't the wireless ETTL perform like the optical ETTL?
Yes... except the wireless (radio) link has greater distance and it is not fooled by external light or blocked by objects.
One of the reason's I started using Pocketwizards in the first place is because the optical ETTL was very unreliable. On several occasions I had very erratic operation with the old ST-E2 optical if there was a lot of sunlight in the room. Umbrellas can also block the signal. It was very frustrating to arrive at a remote location only to discover that your optical remotes won't work reliably. The RF communications has no such limitation.
Now that Canon has the RF communications channel I no longer need to use Pocketwizards.