[This is why](http://www.bogleheads.org/wiki/Dollar_cost_averaging#Dollar_cost_averaging_versus_lump_sum). The expected value means it is statistically better to invest 401k money earlier if possible since the remainder of my savings will go to savings for a downpayment, an account I've got plenty of money to survive on in already (if my company let me, I have enough I could put my contribution at 100% until it's maxed out, but my limit is 50%).
If I didn't have significant cash reserves currently in purgatory before a home purchase it'd be a different situation I guess. But I can very easily take a "loan" on that cash to front load my 401k contributions.
Yes, lump sum investing is better if you happen to find or inherit a large amount of money, but you are creating the lump sum.
I understand where you're at now. You saved cash for a down payment in 2013 and decided not to buy a house (losing potential income from interest). So, yes, the best option at this point in time is to invest that money as quickly as possible. Live off the cash and maximize 401k, makes sense.
But in 2014, you say you will rebuild your cash reserve after your 401k/IRA are maxed, losing potential interest again. Is this the best way to go about a down payment? Each year you postpone, you are losing interest on that cash... What about Roth principal withdrawals? yes there is some risk, but you can budget for a smaller cash reserve, diversifying down payment money. Lump sum 2013 and 2014 roth ira's, reduce your cash reserve by 11k, and use when the time is right. That is my current home down payment strategy. The risk is acceptable because I'm still unsure of when I want to buy a house. From what you wrote, you won't be buying a house in 2014, so you have the opportunity for a full year of investing that cash.
This is more big picture budget strategy rather than month-month budgeting. If you are set on keeping the whole down payment in cash, then reinvesting at the beginning of each year is probably the best way to do that until you make the purchase.