You are right, the guid number of the 600ex rt to the 580ex ii is only two points up, only real difference between the 2 is range, which is far easier to visualise as we all know distance, than the power of technology I dont have experience with.

And yes we all used cameras with built in flash, though you know what I mean.

And there are no direct comparisons between 600ex rt 430ex ii.
So your idea is great! thanks