To answer the original question, I think if you can pull 0.5 g/w with CFLs you're doing pretty well.
Though obviously not as good as HID or T5 fluorescent lighting, CFLs are actually fairly power efficient if you look at total light output/watt energy.
The big problem with these is that the spiral design of the bulbs is meant to throw light in a spherical shape. Even though the bulbs put out a lot of light, in practice lots of the light output gets wasted by being trapped inside the spiral, and (more important) by being radiated away from the grow area.
If you want to maximize yield per watt in a small setup, I think good reflectors are a MUST.
The problem is that good commercial grade reflectors are hard to adopt for CFL use. In this case, because of the rounded bulb shape of typical small CFLs, if that's what you're using, I think the optimal reflector is going to be parabolic (not "batwing") shaped, and something like that is simply not practical to fabricate yourself.
You don't need the whole lamp, obviously, but I think ideally you'd want something like THIS around each bulb to ensure that ALL the light gets used: