I agree with Jo. There is no "penalty" for a 401(k) loan. The "penalty" is interest, which you pay back to yourself, and lost potential earnings. Many 401(k) plans index their interest rate to the Prime rate or LIBOR (sometimes plus 1-2%) so while it's great that the interest rate is now low, a higher interest rate would mean that you were forcing yourself to contribute more back into your funds via re-payment.
Statistics on the typical 401(k) borrower aren't flattering - most end up borrowing more than once, later take actual withdrawals, and have lower account balances and earnings. However, that's probably more reflective of the poor spending and savings habits of those who are typically more likely to need a loan. You don't sound like you fit that profile.
As Jo mentioned, the big risk is that if you lose your job, you do need to pay it back or get hit with taxes and early withdrawal penalties. Those aren't pretty! Another consideration is whether or not you get an employer match - if there is a match, make sure that if you consider reducing your contributions that you don't forgo any match $. If you're maxing out your contributions you're probably contributing at more than double the match rate so it's probably a moot point but worth considering.
At the end of the day, it all comes down to numbers. There are probably some calculators on line that can factor in the length and amount of the loan, the interest rate, you current contribution rate, your average earnings, company match etc. to help determine which will cost you less in the long run.
ETA: Uninformed people (I won't call you out by name) - a LOAN is NOT THE SAME as a WITHDRAWAL. There is no penalty for a loan. Not 10%, not 30%, not 40%. It is not ALWAYS a bad idea to take a 401(k) loan. Please don't answer questions if you have no idea what you're talking about. Obviously we're not all financial advisers but there is no point in responding with misinformation. I have worked in retirement plan administration for more than 10 years. The OP is in a very good position to take a 401(k) loan, it's just a matter of factoring in the small things like her tax bracket vs. interest rate and likely earnings to figure out whether the loan or reduced contributions are more advantageous.