Welcome to the brave new world of dynamic device clocking. 78 usec vs 72 usec is a noticeable, but not massive difference in performance. Since different toolchains are being used, the most straightforward working hypothesis is that there are differences in the generated machine code. Have you examined it with cuobjdump --dump-sass? You can use nvidia-smi to examine whether different clock boosting is responsible for the performance difference. Probably less likely, but a valid hypothesis.
Is the comparison using the physically identical GeForce 740M in the same physically identical system, or are we talking about two physically separate GeForce 740M cards here, or one GU placed in two different systems? Physically separate GPUs of the same type could show different clock boosting behavior even under identical environmental conditions either due to manufacturing variations or VBIOS versions. A specific given GPU may show different clock boosting behavior under different environmental conditions (e.g. ambient air temperature, air pressure, humidity, which affect cooling and thus device temperature) or across driver changes. I am not sure whether clock boosting could be affected by the electrical supply delivered by a system’s PSU, but I think it is least possible in theory.
It is also possible that device temperature and power consumption are affected by different machine code being generated, which can in turn impact clock boosting. Research on the interaction between code execution and power draw and temperature (including effects like local voltage droop and thermal hot spots) and how this can be addressed by compiler code generation is still in its infancy. To my knowledge, today’s compilers usually only include simple heuristics to choose an energetically more efficient instruction when multiple equivalent operations are possible (e.g. shift versus add, multiply versus shift-add). Clealr such static analysis doesn’t cover the complex interactions of a code stream with all relevant hardware components and thus electrical and thermal characteristics.