Average grade of rack pack or wax pack pull?

[swarmee]

You're better off not opening that pack and having the whole pack graded by PSA. Graded packs with star rookie cards are in higher demand than just the card themselves.
It's hard to say what it should grade because you can't really see some major issues (either centering, corner wear, print defects, whatever) through a wax wrapper. You can buy a raw 1984 Topps Mantle for $4, a PSA 8 for $20 or less, and a 9 for $40 or less. If you're pulling for top grades, either open up really expensive stuff from the 60s or early 70s, or cheap stuff from the 90s to 2000s where centering is much better and there's a chance to make your money back on insert cards.
Edit: You said rack pack, there's a better chance of knowing what the card looks like (on one side), and rack pack cards are normally easy to spot corner wear on, compared to rack packs that are normally sealed much tighter. I think you're still better off getting the pack graded.