yfz's are over rated. At first you would just see one here and there, so it was hard to get a good judge on their speed. But now I see one almost every week. Today I rode an 250r and a yfz450 for the first time. The 250r had all the normal mods plus a little port work. The 450 had a pipe and filter. First off I was very impressed with the 250r. I have a lt250r suz with its fair share of of mods, and this honda was faster. I raced my friends banshee that has reeds and k&n. I won by about four quads, WOW! IT sits low and handles nice.
Next I jumped on the 450, very quick but no top end. I personally think the 500 predatory is faster. As for a 450 beating a piped shee, I dont think so. Out of the hole, yes. The first three or four gears, maybe. But if your tuned right you will run one down on a piped shee.