This paper is an inquiry into two kinds of commercial virtue and their epistemic assumptions: maximizing economic efficiency and legal abstinence from interest. These virtues and their respective epistemic domains, despite not being mutually exclusive, have come into conflict with recent neoliberal critiques of Islamic banking and finance. The former, framed in a game theoretical language of problem solving, critiques the latter as engaged in wasteful legal formalism that is bent on avoiding interest through efficiency compromising measures. Although the neoliberal critique is posited as ethically neutral and mathematically objective, I argue that it is sustained by privileging an epistemic context for the calculative techniques of neoclassical economics and its concomitant formation of pragmatic virtue. As I attempt to show here through a comparison of the often overlapping procedural protocols observed in neoliberal and Islamic financial markets, they both presuppose distinct pragmatic selves bound by normative frameworks of commerce. The efficiency standard of neoliberalism, however, reigns supreme in guiding market practices. By treating efficiency discourse as a language game that appropriates Islamic banking and finance as an object of critique within its representationalist fold, I hope to demonstrate how the latter remains entangled, but not embedded or dissolved, in financial capitalism.