Have repelled with 5mm cord using a munter hitch while fully turned out with an SCBA on durning "Saving Our Own" training... I was pushing 270# at the time. It isn't the easiest, but it works fine.

Now, I would rather use this setup:
SMC Escape 8
CMC Escape Line

Anyway you look at it, an emergency shouldn't be the first time you try a new skill or equipment. Practice may not make perfect but having done something before even in training can make an emergency less stressful and safer.