This study examines the extent of the impact of proficiency and language use on sociophonetic variation in Indian English (IE). It is based on an oral corpus using the methods and tools of the PAC project and derived from a pool of South Delhi-based highly proficient speakers. The investigation was conducted using quantitative and qualitative methods and focused on two understudied variables: (1) the fricative realisation of th, and (2) the realisations of the vowels in words of the NORTH and FORCE lexical sets. First, the results demonstrate that a significant amount of variation which cannot be accounted for by the traditional age, gender and social class factors can be explained by the language use parameter. A degree of correlation was found between the volume of use of English in a range of domains, and how speakers take advantage of the sociolinguistic potential of prestigious forms. This offers indications on the location of the leaders of the linguistic change. The second central feature of this study is derived from the investigation of the NORTH versus FORCE distinction. It is argued that the general maintenance of this distinction in IE provides evidence for the endo-normative nature of this variety. In the light of these findings, issues ultimately relating to the debate over nativeness are discussed.