kx 250 piston

It doesn't make it faster, but it reduces friction and may reduce piston weight, I would estimate a .01% increase in top end HP, and a barely quicker revving engine. Unless you are a top level rider, I don't think that you would notice and improvement, and if you were such a rider, then you would likely have somebody on the payroll making this decision for you.

Of course, you should wait for others to step in here, for I did not take the time to double check my facts before posting this. If I later find that I am incorrect, Eric's book is on the shelf, I will edit this post.

In my experience the double ring set ups keep the compression at a good level quite a bit longer. Not sure if you would feel any power gain from only having the one ring.