The integration of a heat pump (HP) with a combined cycle gas turbine (CCGT) to control the inlet air temperature is a promising technology to meet the requirements imposed by the current electricity systems in terms of efficiency and flexibility. If the HP is coupled with a thermal energy storage (TES) in an inlet conditioning unit (ICU), it can be exploited in different modes to enhance the off-design CCGT's efficiency or to boost the power output at full load. Furthermore, fuel-saving would be reflected in avoided emissions. The optimal sizing of the ICU, as well as an accurate estimation of the benefits, is a complex problem influenced by several factors such as the local climate and electricity market prices. This paper aims to systematically investigate, utilizing a mixed integer linear programming (MILP) model for optimal dispatch, the feasibility of an ICU integration in different scenarios (EU and US). Different electricity markets have been analyzed and classified according to the parameters describing the average and variability of prices, the interdependency with the gas market, the ambient temperature, or the local carbon pricing policy. The most favorable conditions are identified and the dependency of the optimal ICU sizing on the climate and the electricity market is highlighted. This paper provides information for a first viability assessment: the concept appears to be highly profitable in hot regions with high price variability. Additionally, even in less profitable conditions (i.e., stable low prices in a cold climate), the system increases operating hours and reduces economic losses.