IBT can really thrash the RAM as well as the CPU:
Before you start, temporarily set the "Stress level" to Maximum, to see how much RAM is available to test. Should be about the same as "Available" value in Task Manager > Performance tab.
Subtract about 200MB from the max to leave some headroom for Windows housekeeping, select "Custom" in IBT, enter your RAM amount and set it going ...
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Am having trouble with the 3770K, am thinking the chip is a lemon. It crashed a while ago after crunching easy WCG tasks for a couple of days with 4.2GHz/1.14V (load), mem at 1333. Am running Windows mem diagnostic with mem at its rated 1600, to check RAM. Have another 3770K crunching hard WCG tasks (3 x CEP2) happily for weeks doing 4.3GHz/1.112V.
CPU #1 (good) is in an Asus P8Z77-M Pro, CPU#2 (lemon-flavoured?) is in a GA-Z77MX-DH3. With the DH3 there are no settings for Uncore Volts ("VCCSA") (to set IMC & cache) or Vtt. Though I've never had to alter VCCSA or Vtt, it's useful to be able to try, so I would not buy a DH3 again. With the P8Z77-M you can even set them from Windows, but the overclock settings in its BIOS are really quirky and it keeps silently trying to turn "turbo" etc back on.