The Accu-stock is a bit stiffer and seems to aid accuracy just a bit.
I have a early 10FP pre-accu-stock but with an accu-trigger.
My son has a 10FCP-K with the accu-stock and accu-trigger.
Both rifles shoot well, but I think the accu-stock gives a bit of an edge because of the stiffness of the stock and the bedding.
There was essentially no price difference between the two rifles when we bought them. The accu-stock is just a newer feature that I would have preferred.