I know this is an indoor thread. with that being said, out doors here plants grow fine and we routinely have a 40-50 degree swing between night and day temps. but in my closet, I like about 10. 78 or so during the day and no less than 65 at night.
Edit: but on a scale 1-10...i'd give it a 1 i mean you don't want your temps going to low or too high so yeah.