the 2500k maxes out temp wise at 72'c so would start to throttle at 70 to be safe.. but it shouldnt crash...
often random crashes can be associated with hpet mode in bios not being set correctly (high precision event timer) it needs to match your o.s bitrate or your system will constantly crash... as soon as the cpu has to run high precision math like 3d gaming. so that may be the root of the problem... the good news is its easy to fix... just open bios, adjust the settings, save and quit. let the dma update and you should be ok...
if this isnt the cause of the problem then as you have already done the basics i would start looking at the psu... get hwmonitor and note down the voltages then ask in the hardware section on toms if there correct.
seasonic are a great brand but like any part in the pc they can become faulty, the advantage of owning 1 is that they are unlikely to take the rest of the pc with it, if it is damaged.
In my old computer it used to shut down under any sort of load. Took me ages to figure out but it was a bad PSU, any load would just cause it to fail and the computer would shut down. This sounds similar, i'd suggest checking that area.
did it crash with the images that you have posted?
If its not heat then
next suspect would be power, but thats looks to be ok seasonic - good, and those readings are steady between load and idle
next suspect after that would be memory, download an run memtest for a long time. Win7 memory allocation is random, which is why it may not be consistent, win XP was not random it would just fill from the bottom up, hence you'd hit a problem at a certain memory load.
could you find out what tempin2 is, seems to be quite a swing for something that is not, cpu, gpu or HDD, if you can't find out what it is can you max out the fans on the case 100% of the time @100% and see if that temp comes down whilst loaded, and whether this improves things. it could be a controller (south I think) and it might be poorly ventilated, might be effecting communication to rest of system and hence causing failures, thats all that I pick up from your second image.
edit: from the first image that 60C on tempin2 is worrying until we know what it is, or control it better.
I tried to run the 3dmark twice the first time with the demo and the bechmark and it crashed, the seond I just ran the benchmark and it did not
I did a few passes on one stick so far with no issues using memtest, I still need to test my second stick, but I got lazy
As for tmpin2, I did some research on the tmpins and they seem to correspond to the core, the sb and the nb in no particular order, it seems to very from mobo to mobo. I am guessing that in my case tmpin 2 is the core as it was so much higher during the processor stress test.