I have an 03' 400ex bored to a 416 with alot of internal work(cams, valves, etc...). Plus it is alot wider than my shee.
This past Saturday my dad and I went up to the track to ride. I wanted to see how fast I was on 4 stroke compared to a 2 stroke. I thought I was going to be a hell of alot faster on my 416 just because it is completly race ready. Well I was wrong, just with a stock shee I could go faster just about everywhere on the track. I could get into and out of the turns alot faster. The only thing holding back the stock shee is the front suspension. I landed so hard with that stock suspension that I broke the skid plate mounting bolts in half. Don't buy Armadillo skids!!! So you should be fine racing mx stock. The first thing I am going to get is probably some Works dual-rate with rezzies.