So, word recently is that the graph is off by 2 cm.
So, accroding to that midsole is really +2, core center is +9.5, and true center is +12.
So, I guess I am 8cm from true center, 5.5 from core center.
These are my everyday skis.  Some some pow, probably lots of cut up snow, trees, groomers, etc.  Mounting foward will help make these skis ski shorter, which will help as i'm around 5'10".  It will make switch better (obviously) and will give the ski more tail for drops.  there is a ton of other stuff as well.
So, haven't really anwsered you question yet.  It depends what you want them for and what size they are.  For everyday +3-+5 is gonna be good.  For more park I would go +5-+7.5.