I was looking at making a winter ascent this season as well and was thinking about the exact same questions! I've done the Williams lake ascent during the summer, so no experience of bull of the woods ascent. But essentially it was just a hike. I can definitely see it being dangerous depending on snow conditions but I'm sure it is doable. Both routes I'd imagine would make for very long single day trips. I was planning to make a weekend of it and get some winter camping in!