I use these liners inside the Spatz Thrmoz gloves, but my friend uses a Defeet one, I think:
This works for me, but he only uses this setup until 32°F and switches to the Sturmfist 4 (I think) below that:
So, I’d hate for you to spend on the Spatz gloves and they’re not warm enough. It sounds like you should go nuclear and get heavy lobster claw gloves or pogies.
Here’s a decent overview of drop bar pogies:
Hope that helps.