Check out the raw numbers for yourself. When upgrading a single generation, you're not going to see anything overly significant, unless you're upgrading from a lower-tier card in the previous gen to a higher tiered card in current gen. But, only you can really decide if the upgrade is worth it to you.
Like Wolfgang said, grab the least expensive of the three. Reading some random forum posts (can't seem to find a review on the "DS" cooler), and it seems that the DS is actually a bit louder than reference. FWIW, reference 5xx coolers are actually quite good. If you really want to get a nice quiet card, go with an MSI Twin Frozr II or an ASUS DCuII. Otherwise, stick with the cheapest EVGA one if you have a particular affinity for the brand.
You've tried each separately? Made sure there was no option in BIOS that you had to select for some random reason? Went through all of the nvidia control stuff to make sure there was no remaining checkbox?
Granted, when I remove one of my cards, I don't really need to do any of that, so I have to wonder if your PSU possibly fried both cards. If both failed at the same time, I would be really worried about what other component caused that to happen, because it certainly isn't just random happenstance.'
@Wolfgang, Whats with the spoiler tags above? Made it impossible to read on my phone.