You are correct, it does affect certain things for sure. I refuse to use Google DNS for multiple reasons - Security (I really don't want them receiving my DNS requests for IPTV), as well as latency. Things you'll notice with a faster (closer) DNS - Way snappier channel changing/zapping. When using the catchup feature, you can skip ahead/back and it will load faster. Also because we are dealing with some kind of TS stream (I think MAG inner portal is like that), your box is CONSTANTLY sending DNS requests for the next several seconds of video.
You can either go on your modem/router to find your ISP defaults, or you can search for DNS close to you (there are a few sites with entire collections of DNS servers by location)
My ping to 8.8.4.4 was 50-65ms
My ping to my local DNS was 5-7ms.
Also, I just set the DNS value in the "network settings" in the Dreamlink settings. I didn't want to set it on my router (forcing all devices to use that DNS)
Anyways, yes it does make a difference for sure.