Hm... It sounds like you're asking if it is better to have your voltages set on AUTO or on MANUAL. AUTO will most certainly be giving your chip more voltage than is needed for stable operation, whereas with MANUAL you can hone in on the lowest amount of voltage necessary for stable operation.
The offset voltage, if I recall correctly, is the additional voltage that will be provided on top of the base voltage (Vcc) when the chip turbo boosts. Again, leaving it on AUTO will probably lead to overestimation of the require voltage while with MANUAL, you can manually lock in an offset. The thing that sucks about MANUAL is that you have to do some trial runs to see what's the proper offset voltage for your chip.