Don't do it.

You have to pay a 10% penalty plus federal and (probably) state income tax. So if you will be in the 28% federal tax bracket (remember it's based on your other income PLUS the withdrawal), and 8% in your state tax bracket, then you will be paying 46% or almost HALF for the privilege. (Figures will vary for your particular situation, of course.)

No matter how you look at it, even if your tax brackets are a little less, that's a stupidly high rate to pay -- it's worse than payday loans!

You'll have to ask yourself -- am I going to make more than that in total return, after tax, on this deal, the first year? It's not 46% you'll have to make, it's 85% total 1st-year return to make it back to the starting line! (You'll have $27K left after penalties and taxes to make your investment with, and you have to make it back at least to $50K!)

If you're dead set on this real estate deal, find some other way to finance it.

check with your 401k manager or call your plan sponsor.
you can stop the amount you are putting in, you may also borrow / withdrawal but you will have to repay it back. if you can get a loan from your 401k it is the best way to go.