I didn't re-pot mine although I think I read that once they show new growth would be the time to do it if that's the course you take. I wouldn't spend the time and resource (soil, etc) to re-pot until I thought it might be worth the investment and if you're in 5 gallon pots prob wouldn't re-pot at all, but that's just me as I'm kinda chinzy & hate wasting anything...I try to recycle EVERYTHING possible that doesn't require an excess of labor/time, lol. I didn't see squat for the first 3 weeks and then they exploded over the next 3. If I were you, I'd give it some more time and after say a month evaluate if the space/pots/soil could be better used on either something else or sticking with it a bit longer. The roots coming out the drainage holes aren't neccessarily a sign of "root bound" btw & shouldn't really be cause for concern at this time; in fact, at least you know for sure she's trying to grow herself back out.
As to the light, dimmible has some practicle uses. For example, 100% on the onset of flowering a tad higher than ideal and then lowering to 75% then 50% allows you to not have to raise the light as often w/o suffering PAR/useable lumen loss or increasing heat or light bleaching. Also, alot of growers seem to like having a milder light when first introducing plants under HID, especially seedlings and "fresh" clones. Its not neccessary as one can manually adjust the light's heighth or simply place small plants lower under the canopy manipulating the shade provided by larger, taller already established plants; but does make this lazy man's life easier here and there. Its infinately easier to twist the knob on the ballast than reaching over the canopy in a closet and "clicking" first one string than the other on the lights, lol.
I think I read in one of the journals that there is a time during the veg period that you can use less than max power but to be honest I think it was someone in the UK that had really high Kilowatt per hour rates cause I remember sorta figuring the difference with my rates and it was so minimal I can't see why you would take the chance to do it, well if you have the energy cost that this state does. 
That's all I got.. 
But I'm sure someone that knows what they are talking about will be able to answer you.....
I read up on it here, in one of the sections and it said that you reduce the root mass of the girl before trying to re veg. I dont think Donpaul does this though? It simply if you have a root bound girl either pot into bigger space like you said or simply reduce some root mass.
LA, you're a GEM!
