Diamond offers customer support both online and via phone. The main method of contacting Diamond for product support is via online tickets. Diamond also offers a toll-free telephone support line (888-238-2272).
As for the warranty, Diamond offers a 5 year warranty on its video cards. The catch (not a big one) is you need to register the product within 30 days of purchase, otherwise it's down to a one year warranty. The warranty isn't transferable should you resell the video card. The official line with regards to aftermarket coolers is they're not allowed and any modifications will void warranty. On the other hand, Diamond doesn't apply any tamper-proof stickers to the screws holding down the cooler and shroud. I was told that as long as Diamond doesn't find any evidence of tampering, the warranty is valid. Users who use aftermarket coolers should retain all of the parts of the original cooler and reinstall it before sending in video cards for RMA. If Diamond were to add official warranty coverage for owners with third party coolers, it would be a big plus and attract more of the enthusiast market.
Overall, Diamond's product support offerings are average, but the 5 year warranty term is great.
Starting with price, Diamond's Radeon HD 7970 Double Black Diamond is one of the lowest priced 7970s on the market. At the time of publishing, it's selling for $420 at Newegg. This firmly puts it in the same territory (or cheaper in some cases) than other 7970s which come clocked at slower speeds. And it's much cheaper than the $499 MSRP for new 7970 GHz Edition (keeping in mind the Double Black Diamond has a higher GPU clock speed, but lower memory clock speed).
Performance wise, the increased factory clock speeds of the Double Black Diamond elevates the performance of a stock Radeon HD 7970 by about 5% on average. In our tests, this helped it catch up to a stock GeForce GTX 680, essentially matching its performance overall. We were also able to overclock our Double Black Diamond further, to a point where its performance was over 9% faster than a stock 7970.
The one thing we wish the Double Black Diamond had was a beefier cooler. Many of the factory overclocked models from other manufacturers come with custom coolers that have better cooling performance and/or are quieter than the reference design cooler. But custom coolers usually result in higher video card cost. The upside to using a fully reference design build for the Double Black Diamond is that compatibility with aftermarket coolers should be good. Our main complaint with the reference design cooler is it's relatively loud.
Altogether, Diamond's Radeon HD 7970 Double Black Diamond video card is a good value. It's priced well for the relatively performance it delivers, and the performance delivered is top end and should please most single monitor gamers who desire maxed out visual quality in current generation games.