Are you referring to the actual core temperatures (as read by TAT) or to the "CPU" temperature as read by most motherboard monitors?
There is plenty of information in
in this article at Tom's Hardware, but the quick answer is this:
According to the article, if you are talking about the actual temperatures of the individual cores, 60C under load is a safe temperature with plenty of headroom. You can go up to 65 under load and still be within what Intel considers a "normal" temperature, safely sustainable for long periods. If you are referring to the CPU temperature (what the article calls "tCase") then 60C is high and you should avoid going any higher.