In general it seems that xc mountain helmets are thicker and beefier than their road counterparts. Is that due to the difference in hardness between sharp pointy rocks and nice, soft pavement? And what about ventilation? Some companies claim that certain vent patterns work well at low speeds for mountain biking, while others are better at higher road speeds. Would a small, light, sleek, cool looking road helmet protect me adequately on an xc ride? Keep in mind that I am not referring to any particular price points, but if I had to I would say around $50. My 3 year old Bell Image Pro is getting pretty ratty and now that I've defected to the roadie side, I am seriously considering a lighter road model, but I don't want to have to get another helmet for xc. I'd appreciate any suggestions at any price. Thanks