Before I got my BB, I routinely slept in my Clark NA down to the 30's with nothing but a sleeping bag. I just zip the weathershield closed a little more when the temp dropped. Not to say I'm adverse to using a UQ on the Clark - actually, I like a UQ better than just a bag, and that is on ANY hammock. And if I had my Clark, and the temp was going to be below 50*, I would want a UQ. I used to have a 1/8 inch aluminized pad that I would shove in the Clark if I got cold, but the durn thing was heavy, and not really needed (for me.) More of a "security blanket" than anything else. Shove a jacket and your clothes in the Clark's pockets, and it does help considerably. But a 30* bag WILL NOT get you to 30* in any hammock, including the Clark.
You have to see for yourself - every body handles cold (or heat) differently. You may need a 0* bag below 60*, or you may be like NEO and be able to get to 15* with nothing but a Walmart pad and a sleeping bag.