Hello @[deleted]
Almost more important than a good video editor and render software, is good hardware. Video and audio rendering is a very heavy processing task, and 4K rendering is one of the heaviest processing tasks nowadays. VideoPad is a great program to edit and render the finished video, but it depends on what it can do with the hardware available. For example, if you don't have enough RAM or a dedicated high-performance video graphics card, 4K quality rendering is going to take a long time no matter what software or settings you use.
NCH recommends upgrading your hardware for this cases on their website. The buffer is essentially rendering in real time: http://www.nchsoftware.com/videopad/kb/1852.html