Good skiers provide a good challenge when bombing I find. Skiing is generally a faster sport. I feel good when I blow by really good skiers that are bombing as well.
I LOVE blowing by skiers especially when you can tell they are really trying to give 'er. My resort has like a 4km long ski-out, so when I get bored of all the side hits and want to bomb, I rarely get passed. I think it probably would be good practice for boarder-x. Other than that I'd say get into really good shape if you aren't, look up snowboarding-specific workouts, a big part of it is endurance.