Metal oxide varistors (MOVs) are employed in surge protection devices, such as overvoltage protection devices, between a pair of signal lines and ground to reduce the capacitive imbalance introduced by the overvoltage protector, thereby improving higher frequency transmissions over twisted-pair telephone lines. The MOVs are sorted into subgroups having a capacitive tolerance of no more than about 1.0 picofarad. MOVs with asymmetrical electrodes can also be sorted to reduce both the capacitance and the capacitive tolerance of the MOVs. The sorted MOVs can then be electrically connected in parallel with a gas discharge tube on each signal line to produce an overvoltage protection device, for example a station protector for use at a customer premises, having a capacitive imbalance that does not exceed about 1.3 picofarads. The use of asymmetrical electrodes reduces the capacitance of the sorted MOVs to less than about 30 picofarads.