I've got an '86 ATC 250R that has a lot of work done to it. Ported cylinder and head, FMF exhaust, big carb, gearing changes and an extended swing-arm. It will launch you off the back at the drop of a hat. It's scarey fast and powerful.
I've also got an 86 CR250 but I don't really care for the 2-wheelers anymore. Had a CR500 at one point but it had so much compression it would nearly break your foot to try to crank it, even with cycle boots on. Had to let it go.
We have a couple of Banshees and a couple 2 stroke 250R 4-wheelers as well. None of that stuff ever gets ridden through.