If you purchased a very rare non-refurbed Mosin in pristine condition, and want to keep it for prosperity or resell then do not even clean the cosmoline off, so that it will maintain it's value.
For the other 99% of refurbed Mosins; it is a rifle, and will never reach it's accuracy potential without extensive modifications. It is in a refurb stock, which almost always guarantees loss of accuracy.
Did you get it to shoot, or are you opening a museum ? Very few fit both criteria. You say sporterize, I say functionalize. A refurb is just not a very functional rifle for shooting sports.