How critical is following mfg's supported memory list?

I have some bad RAM failing Memtest v 2.11.

Board-
http://www.newegg.com/Product/Prod [...] 6813128380

RAM-
http://www.newegg.com/Product/Prod [...] 6820145043

Now, on Gigabyte's website it lists this RAM is being "supported", however after about a month it started randomly rebooting. Reformated/reinstalled Windows XP SP 3 and when I visited IE 8's homepage it didn't even detect that I had Windows installed, even after I activated online. Browser/antivirus software installs were corrupt as well.

I ran Memtest and got a dozen errors after one pass. Timings are correct, and I tried with voltage set to "auto" and manually 2.1, no difference.

My question is is "supported" RAM really any better than "non-supported"? The error-laidened module I got from the supported list was one of the only ones to show up at newegg, the rest either weren't even dual kits or were some off brand I've never heard of.

Why does Gigabyte's website say this-
Memory 4 x 1.8V DDR2 DIMM sockets supporting up to 16 GB of system memory
Dual channel memory architecture
Support for DDR2 1200+/1066/800/667 MHz memory modules

when there are almost no modules faster than DDR2 800 available at a 1.8 volt rating? Or is that just the base rating...

Any ideas or help on this issue would be much appreciated!