First, is this a 4-speed or 6-speed? I think they were marketed both ways in the U.S. While I'm not that sure about 2005, the earlier MC250 models had a 19" rear wheel, CDI unit was the same as the 200cc enduro models (changed the curve of the ignition timing for a harder hitting top end), a 2K2 stator (lighter mass/faster reving flywheel), no spacer between the cylinder and the reed block and at one time I read that they used a different cylinder head but I've never been able to verify that, if true it would probably provide a little more compression. I'm unsure what type pipe would have been used.
My '00 XC250 was marketed as a "cross", it had all of the above but with the 6-speed transmission, 18" rear wheel and FMF Gnarly pipe. At 300lbs (out of the shower) it works great for me. When I first bought it in '01 I was 250lbs and could easily wheelie through all 6 gears. So yes, there are some builds that have some awesome power and performance.
As info, I mainly ride single-track mountain trails (with very steep ascents and switchbacks) and it still pulls great from low RPM's but would probably be quite a handfull for someone much lighter.
For more info check out the sticky post "GasGas History".
If anyone can add anything to my foggy history lesson, please do!
