Upgrade CS6 question

I thought LR always used TIFFs when calling a defined extenal editor. Are you saying that LR4 will use RAW images if a call is made to CS6? Then how can it include any changes made in LR before the call? Surely it does not try to mimic all of the available raw formats, does it? Or perhaps I misunderstood what you were saying?

A second question - how does the ACR in CS6 compare to the (internal) ACR for LR4? Are they the same? Or is one better or more flexible than the others? And, if so, which one?

I had not thought to upgrade from CS5 to CS6 because I use PS so rarely. LR serves for about 98% of my processing and I only need PS for those kind of things that cannot be done in LR - layers, image distortion and other rarely used functionality. I had planned to continue to use CS5 for that but, if CS6 is that much better than CS5, perhaps I should reconsider ...