The ON/OFF current and input capacitance of InAs nanowire based gate-all-around (GAA) tunnel FETs are modeled. Based on the device- and system-level models, optimization has been done and comparison has been made between TFETs and CMOS devices under different constraints for both single- and multi-core processors. Several performance metrics have been analyzed, which shows that optimal numbers of cores, power density and die size area exist for maximizing various design targets.