Bud density is really dependent on type of lighting. In general hps lighting will produce denser buds than cfls. BUT you can still get good fairly dense buds with cfls. the trick is to flower them early. its perfectly feasable to flower a plant under cfls no more than 3 weeks in, it wouldnt matter if it was much over half a foot tall. you will end up with fewer bud sites, but bigger denser buds.
you may veg a plant till its 2 ft tall with cfls, and yes the plant would be bigger and have more bud sites but the buds would all be smaller and less dense (especially the lower ones). with hps lighting you would still get good penetration to lower budsites, so veging more is ok. you can expect the plant to at least double in size when you flower it with either type light.
ery.