OK, first of all on tax brackets:
We have a graduated, progressive tax system. When you move to a "higher" tax bracket, this does NOT mean that all of your income is taxed at that new higher rate. It means every dollar you earn ABOVE that income level is taxed at that rate.
Second, the earnings that you widthraw from a tax deferred account like a 401k is
taxed at your ordinary income rate. In other words, no different than a savings account.
Bottom line is, again, (for your situation) you should NOT use a 401(k) to invest tax-paid dollars. Just don't do it.
Now that that's done with, some advice (whether you want it or not) as you are saving for future goals.
1) Make sure you are contributing PRETAX dollars into your 401(k) at
least to the level that you get whatever matching contributions your employer offers. You are just throwing away money if you don't.
2) Make yourself a budget
with set goals for savings. This budget should include paying off any high interest debt as fast as possible. Make sure you are living within your means, and not increasing debt every month. TRACK your spending for a few months, and continuusly track your progress toward your savings goals.
3) If you are on pace to have a down payment on a house in about 5 years, I personally would not mess with anything other than savings / money market / CDs. Anything else is too volitle, and the last thing you want is for the market to be "down" at the time you want to take the money out for a down payment.
I have first hand experience with this. Trust me, and learn from my mistakes. You can rates on savings / MM / Cds from 4.25-5%. And these rates will likely increase over the next few months.
4) If it's more like 10 years, a couple diversified mutual funds now (actively managed to get more conservative as you approach 10 years) is OK.