So a little update on this. Last batch that I cold crashed in this fermenter I turned the pressure up to about 4PSI. Everything seemed fine, and I had no issues. Filled up the keg as per usual. When I took the piece of wood out that I use to tip the fermenter back, it wouldn't sit flat. The bottom was bowed out! It went back to its normal shape, and everything was fine, but in future I will put just the bare minimum of pressure when cold crashing, and won't be doing any more pressure experiments with my Speidels.