Technically speaking, lowering the frequency should reduce the chance of errors in a CMOS-circuit - IF the circuit doesn't incur any timing violations and the like at this reduced frequency. Lowering the frequency also reduces heat, albeit by a much smaller amount than lowering the voltage would (Voltage relates exponentially to the power dissipation of the circuit, while frequency relates linearly). Lower temperature = less current leakage of the transistors = larger noise margins in the circuit. keeping voltage above spec it shouldn't lead to stability problems unless something gets too hot (for example, the cache part of the i7 Nehalem CPU (I am not sure about the newer ones) do not have temperature monitors, so your temperature might be far out of spec on that part of the die, while within spec on the core logic)
Also you should take into consideration that no two CPUs are identical - there are fabrication differences between to physical CPUs due to the extremely small scale they are produced, so one condition that might apply to one CPU will not necessarily apply to the next (although of course they tend to be similar)