Based on what you are saying it looks like you are better off getting the 5mm pinnacle merino. You clearly state that you want something in between both your drysuit and your seal. I think the 5mm would be the best choice.
I own a complete setup that is Merino linning on everything. I own the ME-7, hooded vest, heated torso, gloves, and boots.
This setup gives me 7mm in the head, 13mm in the chest, 10mm in the groin, 7mm in the extremeties, 4mm in the hands and 6mm in the boots.
The suit is incredibly comfortable and with ease I don and doff in less than two minutes, I kid you not; that's the entire suit from start to finish.
The material to the touch is like no other wetsuit I have felt. It's not rough but smooth, you can tell they used quality when they designed her. I enjoy my dives to be less restrictive than other wetsuits that are so stiff in both the water and out.
Now for the warmth factor it's awesome as it really traps the water and makes it warm in your suit, you can really feel the warmth as your body shifts the warm water moves around and cold water doesn't over power you at all.
I dove 50 F waters in Monterey Break Water for 35 minutes BT and was warm throughout the entire dive; only my hands got cool.
Monterey water is cold as you can feel it nip away on the outskirts of your mask, or when you do a mask clear watch out!!
MG