For me, too far would be anything over about ten to twelve miles. Unless, I had a decent backup plan, a breakdown and a need for repair could turn it into a very long commute. There would also come a point where I would tire myself out so I was actually less productive at work.
Too cold, I couldn't say. I have never ridden in anything less than 24F, where I could just wear street clothes plus gloves and a balaclava. Probably, below about 10 would be too miserable for me, for any length of time. That said the only other alternative is too walk which is colder or get a bus which involves standing still and so being even colder again.