Core i5; which temperature is important?

Core temps always. The chip temp is usually 5C cooler but less important.

Yep, too hot, 73C is the Itel spec for the beginning of long term damage. try to drop the voltage. If your using auto settings, try to stay away from them.

Atrtic cooling fan? You mean heatsink? Which one?

http://processorfinder.intel.com/details.aspx?sSpec=SLB...
Thermal Specification: 72.7°C
Intel Definition
Thermal Specification: The thermal specification shown is the maximum case temperature at the maximum Thermal Design Power (TDP) value for that processor. It is measured at the geometric center on the topside of the processor integrated heat spreader. For processors without integrated heat spreaders such as mobile processors, the thermal specification is referred to as the junction temperature (Tj). The maximum junction temperature is defined by an activation of the processor Intel® Thermal Monitor. The Intel Thermal Monitor’s automatic mode is used to indicate that the maximum TJ has been reached.

IMO, alot of Intel, 1156, 1366 combination's run up to the 70's (core) try to stay south of the low 80's.

thanks guys, really appreicate the responses

oh btw, i'm using hte arctic cooler revision 7. i heard it was a pretty good cooler but ... i can't even oc to like 3.6 without my cores running up to the 80s!

maybe i didn't put enough thermal paste???

Possibly. Maybe you fans are too low, maybe your case cooling sucks. usually it's too much paste. Is your cooler an HDT cooler? Then aplying Tpaste is different.

I look at it this way. I'm in North America and it's winter so even if someone feels that running in the 70's is acceptable how much cushion does that leave you if the ambient temperature rises?

I won't allow my OC'd i7's to run past an average maximum temp of 72C and for extra insurance I set the maximum in the BIOS to 85C just in case something should happen whilst I'm not around.

In my opinion you are pushing it but I'm the type who prefers to err on the side of caution.  

You are talking about case temperatures which, except for a handful of real geeks, nobody has. CPU temperatures these days tend to be measured by core sensors and in the case of the i5-750 for instance the CPU is operating in specification under 99C IIRC.