Our of the 2, the i5-3570k is considerably stronger than the i5-2500. There were several upgrades done to the Ivy Bridge cpus that were missing in the Sandy-Bridge, mainly instruction sets, and L-cache ram, but also extended into exactly how the cpu was oc'd. Ivy introduced the lack of need for BCLK (buss clock) OC, which simplified OC greatly. A i5-3570k will hit 4.3GHz (usually) and require nothing more than a bump to 43 on the multiplier, the rest can be default settings. Anything faster and you'll be digging into the bios to start disabling eco settings, set LLC, and some few other settings in a true OC.
As far as a ram stick just dieing, that's rare. Usually ram, if it's going to die, does so during change. As in the user messed with it physically, tried to OC a cpu (pre-ivy and amd) and forgot the added buss speeds affect ram too, or at times like boot, when you get voltage/current input rush from ram that was previously sitting with no power. I'd be running cpu-z and testing for boot with both sticks individually, forget the game, and try different slots on the mobo with each stick. Make sure bios is returned to default settings (usually F5) before hand.