your I7 920 depending on your CPU Cooler,
Run Intel burn test for 15 runs
http://downloads.guru3d.com/IntelBur...load-2047.html
Its perfectly safe to use on AMD cpus AND Intel cpus
when runnings IBT, set the ram amount to the maximum selection at 15 runs, keep a temp monitor open and watch the temps keep the max aka highest temp on the CPU under 80'c normal usage will never hit 80c IBT uses linpack to stress the cpu about 15 runs of maximum ram = 12hrs-20hrs of Prime 95. but 15 runs will only take 30-60mins. eitherway long as the CPU stays under 80c your fine and can overclock higher if you wish just rinse repeat and use IBT to test stability

if at any time you hit more then 85'c turn off IBT and lower your overclock till you can keep it under 80c
if your on the stock intel cooler dont bother overclocking, something like an OCZ vendetta 2, Xigmatek s1283, Coolermaster hyper 212+ you can safely get to 3.6ghz without much issue depending on ambient temps in your home. Prolimatech Megahalems, Noctua D14, TT FRIO, Corsair H70, etc you can easily get to 3.8ghz more then that is usually luck of the draw.
as for the GPU, for reference my 6970s on stock fan profile hit about 90c when gaming due to them being sandwiched together, thats still perfectly fine, your cards are at 70c or so its extremely cool. for testing GPUs, dont bother with Furmark or anything of that nature, best games to test gpu stability with
are Battlefield Bad Company 2, *great for CPU and GPU overclock testing and stability* and if you need to test with a repeatable benchmark aka just set it forget it and walk away for a bit
Unigine Heaven Bench 2.5, and 3dmark 11 can be looped to run to test gpu clocks etc for stability, as for the 6900 series memory overclocking dosent do a whole lot for performance, so leaving your 6950s memory at stock is fine, *they have error checking go to high on ram and it out corrects itself but it causes performance loss thus push the memory hard on the 6900 series is rather pointless. the core on the other hand you can probably max it within Catalyst Control Center, with the default overclocking tools included, and just set it and forget it. run the tests keep the gpu under 85'c and your fine