Performance wise, the 450 3-1/4 does everything the No.2 does but is a higher pressure round.
Of course, components for the 3-1/4 are easier and less expensive to get but that No.2 shell is sure to impress your buddies.
Since you are building your own, you could of course load either to whatever power you want and the 3-1/4 is easier in this regard. You can literally go from 45ACP power all the way to full nitro loads with the powders and techniques available today. That is more difficult with the huge case volume of the No.2.