I had the local Race Tech shop here install the Gold Valves series II on my KX250 1997. I opted for the series II valves which are intended for supercross and more agressive riders, and slightly heavier riders. Mike @ C&M Suspention is a wizard. I am 200# Intermediate rider, Mike installed the Gold valves, springs, and re-did the washer stacks with his own formula. Night and Day difference!!!!!!!!!!!! Anymore, the first thing I dump money into is not a pipe, wheels, or bars. Suspention!!!! No longer does the front tire jump out of a rut in the cornner.... It is like riding on a cloud no BS! It takes a lot to bottom out, it still will make no mistake, but Mike spent hours with me at the track no extra charge to dial the suspention in. Find someone who knows what they are doing though!!! If the tech you take your suspention to doesn't sit down and grill you with questions regarding your riding style and the racing/riding you do, I wouldn't leave them with him. He will more than likely just go off the Race Tech chart and give you the genaric stack, valving, and oil, etc... a tech who is talented at suspention will sit down and get as much info from and about you, so it can be tailored to you.
P.S.
I started to install the valves myself, but got to a point that I was not comfortable doing on my own ( 97 kx bottoming tubes dont unscrew, the dimples had to be carefully drilled in order to release) looking back it's the best money I've spent, and I wouldn't do it any other way.