RE: Two Questions Caliber and Scope
I would opt for the .308 but I wouldn't have a problem taking the .270 both good cartridges but the .308 has more ammo options available and can shoot heavier bullets.
As for the scope I'm of the opposite opinion of most and think that Leupold isn't a good value for the money. Take a look at the swift line of scopes and yes the Nikon scopes are really nice from what I can tell.
Tom