Hi there, that's a new one to me too.
"Peaking", as described in the User's Guide page 40, is referred to as "enhancing the outline of the subject that is visually in focus". I would assume High Peaking would mean that more outline enhancement is taking place as compared to Low Peaking or Peaking Off. Take a few test shots and see what visible differences these settings produce. From there you can decide which setting you prefer.
Here's a link to that users guide
http://129.33.22.12/release/DSCH2.pdf Hope this helps. :-)
