I am thinking DDR5 is the culprit

Remember that you are pushing the memory twice as hard with every MHz vs the DDR3 on the 4850s
900Mhz = 3.6GHz
1000MHz = 4.0GHz
1100Mhz = 4.4GHz

Guess killed his 4870 almost instantly by going to 1200MHz
http://www.xtremesystems.org/forums/...d.php?t=192696

Thats a 33% increase in memory speeds without additional volts. Be reasonable! So perhaps either a quick death @ 1200MHz, or a slower death @ 1100MHz like I see many people doing?