I had one for a long while technically speaking your KX has better suspenion the CR had the pre cartridge forks (87 model 1st yr) it has the TVC (tension valve control) damper rod style forks. They was good forks but not up to same level of perforamce as your '88's cartridge forks can be. The 86's shock was lacking even back then it required that you stay on top of rebuilding it. The shock body wasn't hard anodized so if they aren't kept up they can wear out and be very expensive to fix. Once again in 87 this was done also along with alot of other things. The motor is good motor lacked bottom end, really strong in the mid good top end lots of over rev. The motor was really reliable hardly had any real issue's with it. Later on had the bike total modified by Pro Circuit, porting/head mods, carb bored out, suspenion modified along with thier trick taper swing arm and square tubed aluminum sub frame bike was alot better afterwards. But technically speakin your 88 KX should still be a better bike it was brand new bike that year from like the ground up. The two most popular 125's that year was the KX and CR's, If I was looking for an old school CR 125 again from that era I'd get at least the 87 model it was all new from the ground up too, new motor,frame,suspenion disc brakes along with some important durability mod's like hard anodized shock body, nikasil coated cylinder, case reed plus even to this day you can still get alot of engine parts for that ride and almost all of the plastic's still threw maier I bet a very fresh one could hang with newer 125's of today. This is just the jist of things but if your lookin at an 86 I could give you alot more reasons on why the 87 was better.