at about what temperature or ground temp. would you use a insulated sleeping pad as opposed to regular

I have slept as low as 10 f many nights and have never used an insulated sleeping pad. I always thought that insulated sleeping pads were kind of a luxury item.

You sleep right on the ground with no pad at all to 10deg?

I would freeze.

Eric,
Short answer, you'll be good. You may get a little chill on the high pressure areas, but you'll survive. If you feel the cold coming through, take a closed cell foam pad in addition to your prolite 4 the next time around (CC on top).
I use a Montbell 90 coupled with a GG torso pad until there is snow on the ground. I only bring my insulated pad when I'm sleeping on snow/ice. In summer I go with just a GG torso and my pack under my legs.
HTH!