I have the 4500 - and it has a power supply box that is a voltage regulator - I would be surprised if it did not do stabilization as well. I've never noticed any issues with the brightness fluctuating.
I would go with the color head. It's diffusion just like the VCCE head, but it gives you more flexiblity. The VCCE head has the grades speed matched, which can be nice.
But what about that really large print you want to make, from that dark negative - you'll want to get the exposure time as short as possible. You will not be able to do that with the VCCE head, your filtration settings are speed matched.
But with the color head, you can determine the filtration settings for both speed matched grading or maximum speed grading. Speed matched grading is achieved by adding neutral density to the filtration setting, to match the speeds. You can run the color head without adding the neutral density filtration for minimum printing times.
See
http://www.butzi.net/articles/vcce.htm for a much more thorough discussion.
(Edited to correct poor use of "B&W" head with proper use of "VCCE", to which I had intended to refer.)
Kirk -
www.keyesphoto.com