Voltage doesn't kill processors, heat as a result of voltage kills processors.
What matters here, is your load temperatures, your overclock's stability, and the stable MHz gains per mV overvolt that your processor sees.
~ When you begin to lose stability as a result of the extra heat which overvolts produce, you are pushing your overvolt too much, and either need to lean off of it, or get better cooling for better temperatures.
~ The "safe" temperature for your processor, is heavily dependant on the amount of voltage you are giving the chip. 2V, with nice 40 degree celcius load temperatures should be safe. 2V, with 60 degree celcius load temperatures is dangerous, and could damage your processor. Your cooling type is largely irrelevant - some people using aircooling in a 15 degree celcius ambient temperature see better load temperatures then many watercoolers do. Watercooling in a very hot room will not be as effective as aircooling in a very cold room. It is the temperature, not the cooling type, which matters.
~ When you no longer see stable MHz gains as a result of overvolting, you should not be overvolting further. Every processor is different, some play well with voltage, and others do not. If your chip does not see gains at high voltages, or dimishing stable MHz returns per mV overvolt start to kick in, your processor is telling you something.
~ It is a myth that each processor has a "voltage limit", a limit that if passed, will destroy your processor. Each and every processor is different, and behaves differently once heavily overvolted. You need to pay attention to the warning signs (diminishing MHz returns, load temperatures, loss of stability) in order to chart out what kind of VCORE voltage your processor 'tops out at'.
~ Nobody can just hand you a number, and say "don't cross this overvolt", with any sort of accuracy or consistancy. Such numbers are complete rubbish, unless that person knows every single one of the variables (overclock, temperatures, stableMHzgain:VCOREovervolt ratio, stability) involved in your specific situation.
~ There is an exception to the "Voltage doesn't kill processors, heat does" rule of thumb: that exception is common sense and logic, as it pertains to overvolting. AMD says that "XXX Voltage is the absolute limit for this type of processor core"; these numbers which AMD gives out are well above the average processor's VCORE limit, as determined by carefully examing the variables which I have explaind above. Most processors stop seeing gains well before such a high overvolt is reached. The numbers which AMD gives to us, more or less represent the limits of common sense. Obviously, giving your Barton 3V of VCORE, will damage it. Most motherboards do not allow such high, unsafe overvolts in the first place.
I hope the above information is useful to your situation. What I have written is not opinion, rather what I have gathered from personal overclocking experience, and the anecdotal experiences of many other overclockers.
