my '01 KTM 200exc is a lifetime keeper bike for me. I have always like the '125' class dirtbike size because i like how nimble and easy to move around they are, but the big drawback is they don't have much down low. The 200 has as much torque as a 250 but nowhere near the top end, in fact, i'm not even sure it has as much top end as a 125 YZ of the same era, but you sure don't miss it. My bike also has a 18" rear and geared pretty short for woods stuff so it feels really crunchy.
i hate riding it on the road, i've got it geard for dirt and besides riding on pavement is boring. its like sitting in traffic in a ferrari. when i do ride it on pavement (its totally legal beagle, lights, plates, insurance, everything) i'm always worried i'm gonna get mesed with by the cops or more likely do some dumb shit like womp curbs that gets me in trouble.
something like an XT250, XT350, KLX250, WR250, DR350 etc are all going to be much more rideable on the street. The lower-output 4T's have less maintenance stuff going on, you don't gotta shift them 4 times before you hit 30 mph, etc.
My brother has a WR426 he keeps at my house, i ride that quite a bit on road, its nice but its kindof a pig off road. I think if i had about 2500 bucks to burn i'd be on the lookout for a really clean KLX250 or DR350.