Hi Tom. Unfortunately, I am not an expert. I did a short search however and some people recommending generating optimized media. In edit menu, right-click on the clip of your choice and from the menu choose Generate Optimized Media. It is going to take some time so the best to make it in advance, but later things should run smoothly.
One more thing, try to have the same Settings of your project and final video as your source file. If you have a recording in 1080p with 60FPS, keep the same settings when rendering. It will speed up the process and also the quality will be better. I hope this will help you, please let me know if you have further questions. I agree, davinci is really good.