shokosugi I believe the sterlings are meant to be built at 8 iron length with their 274g heads. In terms of shafts, I would recommend finding a shaft that you feel will be able to launch your long irons high enough for your liking. Wedges will launch high no matter what shaft in my opinion.
Well, after playing SL for many years it is my opinion that none of the SL clubs work for lofts greater than the 6 iron. And at age 70 I decided to abandon my 6 iron yesterday. So I wouldn't do shaft selection based on long iron desires.