I agree with most of the comments made so far. I don't know what the temperatures are like in Pittsburgh at this time of year, but I believe it is in Pennsylvania, which would be a similar latitude to here (Köln, Germany). I'll add a word or two about winter busking. The first point is that the most valuable asset in your act is you. It is well worth looking after yourself and shielding yourself from the cold as best you can. Good thick boots, which insulate your feet can pay off - as can a good scarf (you do not want your throat to get cold) and some sort of hat. You can lose a considerable amount of body heat through your head. One of the most persistent problems I had in winter was cuts. The tips of my fingers would harden and then split. They then bled over the strings/fretboard and it stung like Hell. The answer is to rub in some sort of handcream before you go out and avoid washing your hands after that if you can. You can get gloves which do not cover your fingertips. It takes a bit of practice to get used to playing with them, but it's worth it, because it helps retain circulation in at least the centre of your hands.
I quite like the sound of phosphor strings indoors, but the thing about Martins is that when you break them (usually at the bridge), you can strip down the end and rewind them around the eye. It sounds quite good enough for busking and I always had a small pair of pliars with me for the purpose.
I one man banded for nearly twenty years and busked for twenty five. Most of the strings I lost were down to my appalling right hand technique. I have come to the conclusion that good right hand technique will save you more strings than any amount experimentation with string type. Using the hardest pick I could helped me to be more aware of whether I was striking the strings correctly or not.
If you think I can offer you any more help, feel free to PM me. Good luck to you.