After doing dataloging my friend found out the knock sensor in Zetec VCT motors(not sure about non-vct) pulls timing because of how hard the head vibrates.
The spike at 6k is caused by that, at 6k the PCM stops paying attention to the sensor and the timing gets thrown back in:
Since Zetecs(least vct ones) rarely knock under boltons or just mild head/cam work you can unplug the knock sensor to get some more timing. On his ZX2 he loged that the sensor was pulling -6 degrees.
