Software-based self-test (SBST) was originally proposed for cost reduction in SOC test environment. Previous studies have focused on using SBST for screening logic defects. SBST is functional-based and hence, achieving a high fullchip logic defect coverage can be a challenge. This raises the question of SBST's applicability in practice. In this paper, we investigate a particular SBST methodology and study its potential applications. We conclude that the SBST methodology can be very useful for producing speed binning tests. To demonstrate the advantage of using SBST in at-speed functional testing, we develop a SBST framework and apply it to an open source microprocessor core, named OpenRISC 1200. A delay path extraction methodology is proposed in conjunction with the SBST framework. The experimental results demonstrate that our SBST can produce tests for a high percentage of extracted delay paths of which less than half of them would likely be detected through traditional functional test patterns. Moreover, the SBST tests can exercise the functional worst-case delays which could not be reached by even 1M of traditional verification test patterns. The effectiveness of our SBST and its current limitations are explained through these experimental findings.