I have both i tell you this much, i climbed a hill on my 250r (86) and i was a bit pissed, because it bogged down i didnt know how to get the power back without flipping it(inexperience). So i had my brother on one of my 400ex got two of them, and i took that up the hill. The 400ex felt top heavy and ackward, the 250r felt planted and very stable, i ended going up the hill at about the same speed on both bikes.(new at riding lol) i liked the r way better. You got to mess with them more but i think its worth it. At least it is to me the 250r rocks, now if you had a 450r i couldn't say becuase i never rode one but, a 400ex come on man, its still only a middle weight compared to a heavy wieght. (off course off the rip you know the engine needs work and he let everything go) at least that is how i would look at it GOOD LUCK PICKING
400ex lsr frame, +2 +4 lsr axle, lsr antifade,+1 1/4 lsr swinger arm +3 atvfourplay lt a arms converted over to take ball joints, burgard +1 antivibe, full hmf, pep fronts, axis rear. aluminium airbox, gibson steering stabilizer (jetted it and put air in my tires)
Whatever it takes