The reason no one uses the K8?

[Nd4SpdSe]

The redline has no input on how much power you have up high. An engine might make max power at 5500rpm, rev to 7500 all you want, it won't make much power there. Pretty sure the K8ZE has the same cams, it just has what you mentioned in it's favor, plus postentially being calibrated for 98 octane in japan.

I'm telling you the known differences between a K8DE and K8ZE, you're just making assumptions. Also what's wrong is that Japan's 98 octane is rated differently. They rate their fuel using the RON rating, while we in North America take the average of (RON+MON)/2