1.8v vs 2.1v is not the same so that is a change. What about P95/Orthos blend test? Try with both. If it can run hours with 1.8v then 1.8v is ok, 1.4v is also ok it it works

If you can run tuned 4x1gb at 4-4-4 requiring 2.1v with 1.8v it is a miracle or motherboard is overvolting big time. I will not be that surprised memtest approves with 1.8 or 1.88 in readouts, P95 is something else and "Blend" torture the real test.
What about Windows update? Does it work? Device manager look neat with no question marks?
About the Dlink I would go to their forum, search model and get an overview. Perhaps they have beta-driver more stable than official - or a certain version is prefered. Actually I would go more by Windows Update than cd from Dlink if it had to be one or the other - but find out what the deal is. They got 64bit driver problem or not? Other people will have same problem. Use whatever works. In general go to site of manufacturer and get the latest - or if you truly want the latest go to chipset maker, like Realtek.
I assume you dont run 4 Windows Tweakers or any other unnecessary stuff after a clean boot? And of course no virus/spyware as well.
What about install cd from Gigabyte, did you go all the way with Ultra TPM, EasyTune?
About Nvidia driver I would just use latest, 181.22. One of those you should not get from Windows update, only from Nvidia site.
Did sfc /scannow find any corruption? and did you remember chkdsk?
Dont really remember details from those dump files but there were nothing surprising in there considering how Vista behaves when memory is faulty. Same old really. If ram has never caused any problem an equally evil part must be able to make same snowball effect of bsods. Think you can forget about dump files - unless new one comes along! All I can think of is weak power supply or bad overclocking/tweaking - but all you changed was motherboard, all parts worked together before so dont know.
Things do break, may be motherboard has a permanent problem but since you just few hours ago started using correct voltage for ram may a bit too soon to point fingers
You do have latest bios and except for memory stuff there should not be need for tinkering. No auto-oc/tweaking/tuning of any kind. Loading "optimized defaults" + ram setup should be enough. You did say cpu oc was limited by ram - and yet use wrong voltage for ram, excuse me for being sceptical and suggesting you run through bios once again, heh. I rarely trust myself when doing this so dont feel offended...
You know best but if any doubt use cpu-z to check settings in Vista.