sswats - C2D's are supposedly resilient to higher voltages, although you do run the risk of reducing the lifespan of the CPU. As mentioned in my previous post, it would be ideal to have TAT temps of 65C or lower, although 70C is not unacceptable.
The best advice I could give would be to weigh up the advantages of a few extra fractions of a MHz (which can offer reasonable speed improvements in CPU intensive apps) against a slightly lower speed with potentially safer operating parameters (ie. a slightly longer lifespan).
As I've said though, CPU's are generally hardy beasts that don't give up the ghost easily
