Dude brevets suck BUT I get a great sense of accomplishment from completing them. Brevets are unsupported Ultra events. Here in So Cal you can't go too far without hills. So our events are very hilly and mountainous as well. 400km is about 250 miles-260 miles (16,000-20,000 feet) depending how they lay the course out. The 600km is 370-380 miles (18,000-26,0000) depending how they lay the course out. I think a respectable times are 16-20 hours and 24-28 hours. Some people are way faster and some slower. Time limits are really generous.