If you're only going to shoot the 50 or 55 gr bullets you can use a 12 twist, but there's no downside of putting a 8 or 9, even a 7 twist barrel on.
And if you ever decide to sell it, you'll get a whole lot more interest with a fast twist than you will with a slow 12 twist barrel.
A 7 or 8 twist 223 in a ti stock with a mountain rifle contour would be a pretty nice build and very useful.
