XC helmet for road biking, or road helmet for XC?
There is significant debate over the statistical benefit of wearing a helmet or not. My guess is most of use wear a helmet just in case the "Helmets are safer' camp is right but wonder if they really are.  

I cannot imagine the difference between helmets from a safety perspective being statistically significant. "Road. XC etc are just marketing terms - the helmets meet standards, and these tell you how much protection you get. Much better to sell two helmets and make twice the profit, easy to do by making them look different enough that peer pressure has people buying a helmet for every task - I bet someone sells a "Commuter" helmet and a "Bike Courier" helmet somewhere. 

You have not mentioned the most important aspect of helmet purchase - fit. A helmet that fits you is significantly better than any stickers as to what standards it meets.  

Presuming then you are choosing from a range of helmets that meet published safety standards, and are happy with the manufacturer as far as their honesty around this (Many standards are declarations of conformance rather than independently tested), choose a helmet that fits first, and has the features you are after second.