250-500cc WR 300 for MX

Is it worth the trouble? I've been thinking about buying an 09 or 10 model and sending the cylinder and head to pro circuit along with getting the CR ignition. I already have a 2010 CR 125, so it would be nice to have a big bore as well.

Or should I go find a four stroke?

Check out www.motocrossaction.com they did a complete build for this bike

I turned one of my'09 WR 250's into an MX specific bike. Here are my starting point performance changes, as I have yet to test the bike and decide if I require anything further.
1) Fork revalve/stiffer springs. I over jump & under jump all the time. I like slamming into those braking bumps.
2) Revised jetting.
3) Drop 1 tooth on rear sprocket, non-O ring chain.
4) FMF pipe.

I doubt I will do much more as I tend to turn my bikes over every year and a half. Not worth the $$

Bobby Garrison won the 2 Stroke MX Nationals at Glen Helen on a WR300 massaged by Zip Ty racing I believe.

Certainly seems like it can serve as a pretty good base for a MX'r!