We present the results of a three year field study of the software development process choices made by project teams at two leading offshore vendors. In particular, we focus on the performance implications of project teams that chose to augment structured, plan-driven processes to implement the CMM level-5 Key Process Areas (KPAs) with agile methods. Our analysis of 112 software projects reveals that the decision to augment the firm-recommended, plandriven approach with improvised, agile methods was significantly affected by the extent of client knowledge and involvement, the newness of technology, and the project size. Furthermore this decision had a significant and mostly positive impact on project performance indicators such as reuse, rework, defect density, and productivity.