Microprocessors with multi-core dies that include bypass buses are provided. Each microprocessor comprises a plurality of physical pins for coupling the microprocessor to a processor bus coupled to a chipset. The multi-core die has at least two complementary sets of one or more processing cores, each providing a bus interface coupling respective core inputs and outputs to corresponding processor bus lines. A bypass bus on the die enables cores of the complementary sets to bypass the processor bus and communicate directly with each other. The bypass bus does not carry signals off the die, drive signals on the processor bus to the chipset, or receive chipset-drive signals from the processor bus. Moreover, the microprocessor is operable to detect whether the chipset or a complementary core is driving the processor bus, and if the latter, to select the higher quality bypass bus signals over the corresponding processor bus signals.