"rightly or wrongly I assume that 1 cup of flour is equal to 8 ounces or
228 grams"
That would be wrongly :-) A cup of flour weighs 4-5 oz. Using 8 oz. would
yield very stiff dough and very dense loaves.
"Is the difference between 11.8%, 12.5% and 13.2% in the end product
discernable?"
If you can get your hands on bread flower, in the 13% range, I would use it
for artisan breads. Because you won't be using a pan, the extra gluten will
help.
On the retarding question, I do not adjust my formulae. I find retarding
not only makes the scheduling easier, it greatly enhances the flavor of my
bread.
Just one man's opinion :-)
Kyle