JJ,
The 10 Speed portfolio is only 20 percent fixed income (TIPS and International Bonds) so most advisors would consider it pretty aggressive unless you are expecting to have other bond-like assets such as a corporate pension. Also, both TIPS and International Bonds can be volatile and the purpose of building a ladder is to avoid volatility by having scheduled maturities--- that way you'll never have to sell in the down market.
That suggests that you should have $80,000 to $200,000 in a ladder--- since each $40,000 is 4 percent of your portfolio, your fixed income allocation would increase in this way as you increased the ladder:
No ladder, 20 percent fixed income
1 year: $40,000, 23.2 percent
2 years: $80,000, 26.4 percent
3 years: $120,000, 29.6 percent
4 years: $160,000, 32.8 percent
5 years: $200,000, 36.0 percent
Note that it would take 4 to 5 years of ladder to get your fixed income allocation down to the typical level of endowment portfolios and balanced funds.
Scott