Re: Memtest+ slacking......
When I build a new system (in process of doing so now), the first test I run is memtest86 at various settings/speeds to test the limits of my memory and see if the memory is faulty. Memtest is good for that. I'll run a couple of loops of the whole test, then 10 - 15 rounds of test #5, because that's where I always tend to get errors. Then from windows I run orthos. Like brandito said, it also stresses your memory along with your cpu of course.
Personally, I only run these tests for an hour or so. I've never found it necessary to run them longer, i.e., my systems always have run stable so long as they've passed an hour of memtest86 with plenty of runs of #5, and an hour or so of orthos. Others may jump on me for that statement, but that's been my experience.
Gigabyte P55A-UD4P, Core i7-860 Lynnfield at 3.6GHz, ZALMAN CNPS10X QUIET 120mmCPU HSF, CORSAIR Vengeance (2 x 4GB) DDR3 at 1640, PowerColor HD5870, Earthworks 650W PSU, Kingston HyperX 120g SSD (W7 64-bit), 1TB Black Caviar storage, LiteOn DVD burner, Antec 902 case [B]
ASRock Z68 Extreme3, i5 2500K OCed at 4.5GHz, CM 212 Hyper Plus, G. Skill Ripjaws 4G X 2 2133 Ram, WD Black Caviar 1TB OS drive accelerated via RST by 60G Mushkin Enhanced Chronos, 320 WD Blue Caviar, unknown DVD drive, MSI GTX 560 Ti OC, PC Power and Cooling 610 Silencer, old Antec Super Lanboy case, LG 22" monitor, Win 7 HP 64-bit