UPF 30–49 blocks 96–97% of UV radiation, which is very good protection and works well for most skiing situations. If you're skiing at moderate altitudes during typical winter conditions, this level of coverage will keep you well-protected on the areas the balaclava covers.
The main time you'd want to step up to UPF 50+ is for high-altitude skiing above roughly 8,000–10,000 feet, spring skiing when the sun is stronger, or if you have fair or sun-sensitive skin. Snow reflects up to 80% of UV rays, so exposure adds up faster than you might expect on bright days.
For the average resort skier on a typical winter day, UPF 30–49 hits a sweet spot. It's plenty of protection for most conditions, and you can always add sunscreen to any exposed areas for extra insurance on longer, sunnier days.