My comfort range is around 25-90° F (-4-32°C). I can ride any distance at my normal pace in that range. I rode 50 miles both yesterday and today at right around freezing. Below ~25 I use a different bike and different clothes so it's much slower and my rides tend to be shorter. I'm good down to around zero (-17°C), but when it's that cold, I can't stay out for more than an hour-and-a-half or so, and it's pretty unpleasant the whole time. I don't go out below zero anymore other than my one mile commute to the train station. Above 90 I'm fine up to as hot as it ever gets here as long as I back off the pace and drink enough water.