Well, I just learned yesterday that Pro-X is in fact the same thing as OEM. They are the same piston as what you buy from Kawasaki, just sold under the Pro-X name.
With that being the case, I went with a Wiseco in my 2000 KX-250. I think I also have a Wiseco in my '98 KDX-200?!?!?!?!!?!?!
As for Wiseco, just don't start it up like a motocrosser, i.e., let the thing warm up a little before you get on the throttle! It definitely needs some warm up time to let everything settle in and expand as the Wiseco piston expands at a different rate, i.e. faster than the jug.
I have never seized a Wiseco piston, but then again, I always let the bike warm up before I start twisting the go-grip!
Hope this helps.
David