I'd keep the 300. You can always load it up and down for other uses (other than big animals) and the extra 1 3/4 lbs isn't all that much.

Don't get me wrong, I like light rifles, and think the world of the .280 ... but I guess I'd keep the thing a little while before I decided to off it right away.

But hey .. it's your money and rifle ... do what makes you happy.