Those are excellent temps. My 3 Ghz P4 at 3.5 Ghz goes up to 64 C under load at 1.575 set in the BIOS.
As to the lifetime of overclocked CPUs, don't worry. If you don't raise the Vcore to over 1.65 V, your CPU will very probably last for many years.
I've been overclocking Intel CPUs for years and have never seen one die.
My friend has been using a 300 Mhz Celeron at 450 Mhz (with an increased voltage) for about five years now.
And yes, Abit boards do show much higher temps than, for example, Asus boards. I think Abit measurements are right; Intel chips have thermal diodes right inside the chip, so don't be scared of those temps. Intel's own specifications say that temps up to 68 C are acceptable. Although I wouldn't go that high.