There is no practical limit, but you might have to go to extremes with gear. I ride about 25 minutes one way on my commute. If it gets below freezing, my hands get painfully cold. If the trip were longer, it would be worse. I've ridden in 18 deg F (-8 deg. C) and that is very cold for me. I don't use a balaclava, but I do use a knit cap under my helmet. When it gets below freezing, I usually have on a shirt, sweater, down filled vest, coat, and shell. My body stays perfectly warm but my hands never do. Oddly perhaps, my feet stay warm, as well as my legs, but I am always at least moving my feet. I have tried frequently taking my hands off the bars and moving my fingers and this seems to help a very little, but not much at all.
For me, there is no glove I have yet found that can solve this problem. Had a pair of arctic mittens once a long time ago that would stand up to any amount of cold, but haven't tried mittens on the bike. Not sure you could use them on a bike. The last pair of gloves I got was a pair of Ice Armor Ice Fishing gloves with a gauntlet cuff. Still not warm enough. I am willing to try a set of mittens if anyone has a suggestion, but after that, I am either going to live with it or go heated. My hands are the weak link for me.
Jamis Commuter 1.0/Xtracycle Stokemonkey 36V LiFePO4, 15 ahr
Giant Boulder 9C 8x8, 48v, 10 Ahr LiMn from ebikes.ca