Instead I am thinking of putting it in a taxable account, where I could have access to it if I needed it. (Eventually I might use some of it as a downpayment on a house.)
If there's a possibility that you will need access to it (for a house or anything else), I wouldn't put it into your 401k.
Whether or not to max out a 401k before investing in taxable accounts is an ongoing debate in several circles and it can get *really* ugly (been there, yelled that). Basically it all comes down to math and you are the only person who can make that decision because it depends completely on your personal situation. But from what you have said, I would to the taxable just so you can access it if you need. And tax diversity is a good think anyway.
Also, your returns won't necessarily be higher in a tax sheltered account, they'll just be taxed different. And when you take into account that with taxable investments you get taxed 15% on LTCGs rather than the whole thing being taxed as income (as with a 401k) a case can be made for taxable investments.
Basically, it all comes down to math.