Hey Greenco, I would go with the Bridgelux Vero 29, the packaging is much better and will save you time and money in the long run, the Cree's are I think about $10 or so cheaper per LED, but you have to ad the mounting bracket into it and a few other things.
You are going to be getting about 40,000 Lumens from the 4 LEDs, a 600 watt HPS spit out about 90,000 with optimum setup. With the LEDs almost all the DC Flux or Lumens are in the beam angle already (100-130 degrees), with a HPS a lot more then half of the light needs to be reflected back into your beam, that's why vertical growing with HPS is almost impossible to beat, you are using 360 degrees of the light.
Anyway, I would imagine you would use the 2700K Vero 29s, the ones with 80 CRI and 9380 typical Lumens. You could possible add one extra 5000K a little above everything to keep the plants shorter.
Its really hard to say, but if you wanted to do a run with just two of the 2700K, 80 CRI LEDs, you might be surprised, they have a much much higher CRI then the HPS bulbs, lots of people including the film and photography industry are having a hard time adopting LED lighting. They say, even using LED lights with high CRI will produce prints way outside the color parameters they wanted to get. I think the main problem they are having, as well as growers using LED lights, is the multiple point sources of the actual light. People make these LED lights for growing, with 100s of little LEDs, I think all the individual light sources mingling with each other is fuking it all up. Its the same sort of thing you see in pro sound, those huge line arrays they use at large venues have to be finally tuned, so all the speakers are working together, or you would have large areas in the crowd where it would be either, too loud, not loud enough or just sound like mud.
How did you want to drive these babys?