Tapered sitka spruce comes in at about 600 grns for my 59 lb bow with 125 grn point.
Dan, I don't know where you're getting Sitka Spruce that heavy but Sitka is lighter in weight than cedar. My 70# spined tapered Sitka arrows are 575 to 580gr cut to 28" BOP with
205gr headsI've used POC shafts since 1951 and have shot them out of bows up to 125# @28" and never had a problem with them being too light in weight. Shafts like that are hard to find nowadays but there are some good one's around if you know where to look.
I just recently talked to an old customer in his 80's that had a couple thousand old Acme Premium shafts that he wanted to sell, still in the box that he had purchsed over 20 years ago.
I told my arrow man Paul Jalon about them and he picked them up and will be sharing the wealth so to speak with arrow customers.
There's other fairly good arrow woods available but for the best of the best, you can't beat good POC IMHO.