I'd put it in the 401K. Your spending could be lower than projected, you could move, tax rates can change (such as a lot of the 25% bracket becoming a 22.5% bracket in the near term). All of these things can swing both ways of course, but 34% is a pretty big savings today.
Luckily, we're only talking about a little under 2% of your total investments, so even if you pick wrong for these last $24K deferral dollars, you're gonna be just fine overall.