the surgeon i spoke to instantly said that he wanted to BSSO my mandible at least by 12mm, because any less would not be worth the effort, pain and recovery. i think DO plays more of a role if you are looking at advancements north of 2cm but unless you look into the mirror and a severly deformed person is staring back, don't bother looking into it.
DO is great for teens though, because you can dynamically advance along the natural growth of their maxilla. for adults, BSSO is the gold standard.