I just recently completed a build with an i5 2500k processor, z68 asus motherboard and a stock cpu cooler.
After booting up for first time and installing windows 7, I ran prime 95 and got temps very quickly into the 70's and 80s(at one point reaching 87 degrees. I have now removed the cpu cooler and reseated it with artic silver 5. After doing so, I did a sensor test(using prime 95) with real temp and temps did not exceed 70 (67, 70, 69, 67). I also idle at around 34-38 degrees(similar to before the reseating). Are these now good temps?
Well I just ran Prime 95 for approximately 40 mins and the peak temp was 73 degrees(70, 73, 72, 70). This seems high compared to other reports on this website for the 15 2500 K. I'm OK with these temps as I probably will never use the CPU as much as this, but I want to make sure that my CPU running at slightly higher temperatures is not going to result in a shorter lifespan for it.
Also I want to make sure that the above temperatures are OK.
Those temperatures are completely normal for prime95 with the stock cooler. No reason to worry at all. In heavily loaded apps/games you will probably be around 50 to 65c max, and how much of the cpu's life would that be, 20 percent or less? Most of the time you'll be running under 50c so i wouldn't worry. Your chip should last at least 3 years under the conditions you explained, most likely a lot longer.