I like hunting rifles that balance at the front action screw or that are slightly muzzle heavy around an inch or two in front of the action screw. They tend to settle better for offhand shooting you have to do sometimes hunting. Just cutting a barrel to 18" will often times make your rifle butt heavy which isn't what I like to carry. My opinion as well slings should be shooting aids more than useful for carrying your rifle.
Both of the points are good general shooting points, I was trying to address how to lighten the burden the OP is feeling from carrying his currently rifle all day.
Very thing is a trade off, one feature is given up for another, to strike a balance that meets the shooters needs.
Balance point is a matter of personal preference, mine generally is centered about the chamber area. I hold my rifles with the lead hand just in front of the magazine. It is about getting the feeling that the shooter likes, sometimes adding a little lead into the front of the stock really helps.
I agree that a sling can and should be a great shooting aid, Though most hunters do not under stand how to properly use it. Once again compromise.
As for barrel length, between 18" to 22" seem to be the happy medium for most none magnums. The effect of shorten a rifle may be more mental than fact. That said, the "feel" of something is subjective, to me compact rifles carry easier.
At one end I have a 8X57 Mauser with a 16 1/4" barrel , at the other end I have a 26" barrel 308 rifle that weights in at over 14 pounds. Love them both.