I'm researching with my son for a long-range target rifle for his HS grad present. While his .223 is capable, he wants a larger boolit better suited for LR.
His first selection was .243...certainly a capable contender for the stated objective.
Downside is that it is a bit of a barrel-burner. I'm told- around 1/4 the life of a .308 barrel.
That said, we all know there's a lot of variables (loads, not shooting the barrel 'till burn your hands, etc.), and barrels are like tires- but given your stated objective of a truck gun/varmint gun; seems that a caliber with better barrel life should be considered.
FWIW, we have decided on a .260...
Extremely flat shooting, and easier on the throat. Commercial ammo is scarce, but I handload so that's not an issue.
Why not a .308? Extremely versatile, capable of reaching out and touching whatever you want- at whatever range you want- and there's no question about the availability of a wide range of commercially available ammo.
For your intended purpose, this would be my choice:
http://www.ruger.com/products/gunsiteScoutRifle/models.html