I use a GC 3 mil core warmer under my 5 mil HS when it's cold. Warmth of the GC, with the comfort HS. That gives me 8 mils on my core with 5 mils on my extremities. I've dove wet down to 53 degrees with this set up. When the water gets warmer, just leave the GC off and your still OK. In the pool, I just wear the GC. Very versatile system. The only drawback is with the HS. It's SUPER comfortable, but velcro sticks to it and it pills like crazy! It's really only a concern if you care what you look like, which I don't!
Good luck!
~Steve~