3/32" would be great for that blade. Would make it one slick cutter. I actually have a 5.5" blade in 3/32 O1 and that sucker takes some serious abuse. I've batonned the living daylights out of the thing with no ill effects. Just don't pry with it! That thickness should be fine for a puukko. 1/8 would be okay, but for a knife designed for cutting, like a puukko, 3/32 would do great.