One of the great things about the Stevens and Savage rifles is that you can change barrels yourself. I'm not familiar with Pac Nor barrels, but generally speaking after-market barrels tend to perform better than factory barrels.
Before I changed barrels though, I would encourage you to get a better stock than what comes from the factory on a Stevens. Then I would have the action bedded.
The rationale being that you have a pretty good chance of getting a decent factory barrel that will shoot 1moa or less.
I can almost promise you though that the factory stock is a piece of tupperware - meaning you will be able to twist it. That's not a stable platform.
A decent stock, like an HS Precision, will cost you $200~$300 dollars.
Here's a write-up of another rifle of mine: My 280 - Updated!
It has an HS Precision stock.
As an FYI, I've given you links to my rifles because both projects started out much like you are. I wanted a rifle that got me into the game right out of the box. From there I built and built...
Here's the break-down on my 308.
SSS Stock: $300
Bedding, crown, trigger: $250
Total: $1265 (holy crap...this is the first time I've added it up)
I now have plans to add a muzzle brake and have the lugs lapped and bolt face squared.
Like I said before, it's an addiction.
In terms of a rate of twist for a 308, Remington cuts their barrels 1:12, Savage cuts 1:10 and not long ago I read about a rifle with a custom barrel that was 1:11. Generally speaking, the heavier the bullet, the faster you need to twist the barrel.