Hey guys, bit of a lurker here, but I haven't seen much info on the 2mm overbore, so I wanted to share my experience. I have an 06 WR450 that I picked up used, and after a year of hard riding it was in need of a new piston, rings, and a cylinder hone. I decided to get a 2mm overbore since it wouldn't cost any extra, and it brought the displacement up to 472cc. Got the parts back from Millenium Powersports and it was a straightforward affair to redo the top end. The results were immediately noticable. The few extra CCs don't make a huge HP difference, but the behavior of the bike definitely changed for the better. The bottom end got some more oompf and I was feeding the gears much much faster as it would climb the revs quickly. The power doesn't overwhelm you in the slow technical stuff, in fact I felt like the bike was more resistant to stalling since the motor had an easier time keeping the flywheel spinning. Definitely a mod I recommend, especially since if you need to hone the cylinder, you pretty much do this at the same cost.