tastewar pointed out this video, about DVD reissues of TV series that squeeze more than two hours of video onto single-layer discs.
The first disc in the 5-disc Kolchak: The Night Stalker DVD set I bought is about 7.5 GB. So, it’s a double-layer disc, and I’m assuming all of them are. The video quality really is quite good, considering the source material.
There is one tiny technical quirk that can show up, especially when credits are overlayed on the screen. You’ll never see it, unless your player supports 24 frames per second on DVDs. If it does, you can almost certainly disable it.