You seem to have your evidence right there – no need for any theoretical discussions, Google is using the dc:title. (My guess is that is displaying that one rather than the <title> because the <title> is just a keyword-filled spamfest, not a page title). As to how they compare when ranking the pages, that's difficult to tell, because there are so many factors that feed into the ranking algorithm. If it thinks that your dc:title is the actual page title and the <title> is a load of rubbish, my guess would be that that's how it will treat them in the ranking as well as in the display, but I've not seen any research into it.
Any posts I write in Arial are on my mobile phone, so please excuse typos etc. Any posts I write in Verdana are on a PC, so feel free to berate me mercilessly for any mistakes