My X61s is sick...

[precip9]

I have three X61s, all configured with Windows 8.1. One freezes.

1. They all have the Middleton BIOS, and identical 5300 wireless cards. There are no clock mods.
2. They all have 8GB of ram, purchased off eBay. Out of five sets purchased, one was immediately bad, but not this machine. The W8 memory test passes with no error. But I've never had a memory test that could actually detect bad ram; pattern sensitivity makes this difficult.
3. The freeze is so sudden, there is no flag on reboot. The OS doesn't appear to know it froze.
4. It is the only one of the three that has an SSD.
5. It happened before the 8.1 upgrade.
6. Mentally, I associate the freeze with upgrade to the Intel 16.1.1 driver. I also associate it with wireless activity. But the machine is lightly used, and almost constantly on wireless. So these are probably meaningless "feelings."
7. No other "funny business", like file or screen corruption, or boot failure, has occurred.
8. When it freezes, it takes more than the usual 10 second power button press to restart. More like 30 seconds.
9. The card reader is broken; probably irrelevant.

Now we have the usual suspects:
1. Wireless card.
2. SSD
3. RAM
4. motherboard
5. Bluetooth card? This machine does something odd. Every once in a while, it loses the Lenovo bluetooth mouse. The mouse is restored by cycling the bluetooth radio off/on.

Seemingly eliminated: OS and drivers, because the other machines work fine.
Any interesting experiences/resolutions out there? Any memory tests, preferably on standalone boot media, that will beat the ram mercilessly?

[RealBlackStuff]

Most likely you bought no-name RAM or RAM from a no-good eBayer.
Both can be equally bad.
So what did you buy and from whom?

As for testing the RAM, use the one and only Memtest86+: http://www.memtest.org/

[precip9]

Considering the reports about name-brand RAM, 5 good pairs out of six isn't bad. I'm not going to name them, but I will run memtest86.