Based on the property of angular dependent transmission probability of electrons observed in graphene PN junctions, a modified MUX-based graphene logic device is introduced. A more elaborate resistance model including ON resistance, leakage resistance and contact resistance is given as well as a capacitance model of the device. Compared with Si CMOS switches, MUX-based logic graphene gates have potentially lower output resistances and a smaller device area. Since interconnects play an ever increasing important role in digital circuit, for the first time, module-level and system-level analyses are made for better evaluating the potential performance of graphene logic devices. Based on the analysis of a 32-bit Han-Carlson adder, module-level evaluation has been done and comparison has been made between graphene logic circuits complemented by multilayer graphene interconnects and CMOS logic circuits with Cu/low k interconnects. The results indicate that MUX-based graphene logic circuits can outperform CMOS circuits in terms of both delay and power consumption. Both devices being evaluated are based on the 15nm technology node. For the system-level analysis, the graphene logic system can have 50% higher throughput than its Si CMOS counterpart with the same power density and die size area.