Your claims don't line up with my tests :/ Maybe you need to rerun things under more controlled circumstances, or check to make sure you've got your meter properly calibrated.
+/- 200 means a potential spread of 400K from a fixed point - depending on where I pulled white balance, at most I could get around a 450K split, but usually closer to 350-400K
I couldn't go to 1:64th or below for my tests, but I found the 600 performs much better than you claim, and within the published specs at least 1:1 on down to 1:32 power.
Rock solid color and output stability within a fixed power setting across each setting.
This is a comparison of 1:1 vs 1:32 power. Just sequential frames, bare bulb, from 10ft away; adjusting only aperture, keeping ISO and shutter speed constant.
If the 600Pro is an improvement on this, that's fantastic, but it's already really, really good.
One thing to keep in mind is that the spec's on paper, does not always reflect the real world performance.
Considering the AD600E states a tolerance within +/-200K which is not true at all.
It's rather 800-1000k from low to high. The tolerance from pop to pop is however acceptable within 100k.
Now it's quite possible the color stability is improved, however, if their previous specs. is any indication i would take that with a grain of salt.