standard chain vx. o-ring chain

The bore size has nothing to do with the chain type imo. You can install a o-ring on your kdx and will probably not notice any power difference. It will create a little more drive line loss, but not much. An X-ring chain causes even less loss than an 0-ring. I get 2mpg better on my street bike with an X-ring over the stock 0-ring. I had an 0-ring on my KDX (this was before x-ring's were popular) and couldn't tell a difference. On my YZ125 I tried an o-ring and could just barely percive a difference, could have even been my imagination. I'd recomend an x or o ring for the KDX as they are lower maintance and last longer:)

Use an x or o ring chain on your KDX. You will not notice the power loss if any. Put the new chain on with new sprokets and not only will you not have to adjust much, but your sprokets and chain will last for a long, long time. Ride safe--John