Has been debated at our Club on numerous occassions.
Based on cloud OVC, SEP IMCR PPL, we reakon 1800 feet over land. The situation is an emergency, which when in cloud could lead to distraction followed by loss of situational awareness and associated loss of control. Any passengers in the back are going to panic big time and will distract the PIC.
Coming out the bottom of the cloud without an engine / or fire without the view of a landing site is going to test the best. Worst case could see the a/c well out of straight and level.
We based 1800 feet on a real emergency event where the a/c was close to being inverted and needed all of that to recover.
It's all down to experience and is therefore subjective. My CFI told me that I would need 1800 minimum feet given my experience and as such if it OVC for the route, I want 2000 feet to play with (I'm hopeless at forced landings).