OPSPECS by definition are a Part 135 Function. Just like Management Specs are a function of Part 91K. OPSPECS don't require an SIC. The SIC requirement comes from the Regulations for Passenger carrying IFR Part 135 flights. The OPSPEC that pertains to this reg. actually is an exemption to the rule if you have a working autopilot. (Auto-pilot in lieu of SIC)
Therefore, any Part135 flight department that carries passengers under IFR requires a SIC. Unless, you have the specific OPSSPEC.