if you want to go fast you need bigger wheels and better bearings. big wheels means that you need more clearance to prevent wheel bite witch BTW wheel bite at 15 mph is not fun. so if your slideing get a drop board. but since your new to it I suggest a long (like 48") symmetrical board. big low duro tires and like reds space balls.
sorry for the slow reply, i haven't been on here in a while and i don't think many people have either. so are you looking for strictly downhill, or maybe some sliding here and there, or an all around board that you can commute with too?