After creating my first subsurface entry, my performance dropped drastically, with stutters happening.
Of the 16-18ms/tick update times, Subsurface appears to take 6-8.
Edit: Might be a duplicate of https://mods.factorio.com/mod/Subsurface/discussion/6869df7fe53b471a55afb877 as the issue only happens when the miner I was using was causing pollution. I'll try other pollution making techniques.
Edit 2: Small burner generator doesn't cause this issue, nor does the hauler. My deduction is that it's something specifically related to a special interaction with the Miner vehicle. I'll try KingJo's bulldozer.