Associates on tracks that have different expectations for them as to billable hours

At a panel on diversity, reported in 8-K, Vol. 4, Fall 2008 at 18, a partner from Patton Boggs, Mary Beth Bosco, explained that her firm has three tracks for associates, based on the hours they are expected to bill. One track is for 1,650 hours, the next for 1,800 hours, and the third for 1,950 hours. All of the tracks are considered full time and Bosco claims that associate are all eligible to make partner. Hogan & Hartson, also represented on the panel, has a two-tier hours track for its associates.

Should a law department try to choose as its core associates on matters those who are in either a high or low track? Would invoice data reveal that higher-billing track associates tend to bill more time at the same call, meeting, or conference than lower-track associates?

Partly I feel this question is similar to whether law departments should care about a partner being an equity partner or in non-equity partner (See my post of Sept 5, 2005: non-equity partners.). The issue is quality of work in relation to cost, not titles or tracks.