Just took a interested read of this, Hi Pilgrims BTW.
If you were, sadly, to go down (I think you won't), then Williamson would make sense, but not if you stay up. Hear me out.
We went for the young up and coming lower league Manager, when we had a decent buffer, which we have needed all of while he gets used to the Championship. Yes, we were starting to panic but it's turned out well, so far. With all possible respect, I don't think you would have that luxury, if you're at this level again so I would try for someone like Rowett, once Mowbray is back at Birmingham. He's a good Manager at this level and should be available.
If you did go down, you would have more than enough time for Williamson to settle and still be comfortable.
Another very good Manager, that would keep you up again is our Nige but I'm not sure he will take another job after a couple of health scares. Believe me, he's nowhere near the miserable SOB he's portrayed as and really knows the game.
Stay up- Rowett
Go down - Williamson
Just my opinion.
Good luck in the next 2 games.