The Zook has better bottom end, but they are both fine machines. Unlike the CR and YZ, they both have powervalves. One thing to remember, the RM's outside rear brake pad isn't exactly held in place, and can wear down enough that it simply falls out. I also have never liked that way that the right side shroud is a part of the fuel tank. It could easily stall from fuel starvation long before the tank is empty. The KX cradles the tank inside the frame. If you don't like the gearing, you are more than welcom to buy a new sprocket that better suits your type of riding. The extra ring may provide better sealing at the expense of more friction. I would say that it is a trade off, and with the engineering that has gone into all MX bikes, it has little effect in the end if it is kept stock.