So, I have a pretty Beefy computer. Rtx 2070 with a intel core i7-9700k and 16gb of Ram. But lets say when I run a clip, it runs fine. I split clips then run them it skips frames (Doesn't leave like 5th frame from ending the first clip) I can barely even run this at Quater quality.
Is it a game capture video with 18k ultrahd resolution, and 189 to 280fps variable framerate? Or is it a DV-avi from an ancient camera with 720x576 50i resolution and fixed framerate?
Try to use Mediainfo, and post file properties too.
It's just CSGO Clips off youtube. Like.. 300 FPS 
No clue on how to use MediaInfo though. Sorry
1.The person in that youtube video edited those clips like a charm. So I don't think the clips are the problem.
3. https://mega.nz/#!iRkDxByT!yEcX4H1TRyZEA2qmKjxVKuFyAmnPlNEOYgsFaKrpLu0
4. geforce rtx 2070
5. 25.21.14.1735
6. Yes on my GPU
8. I'm using the standard render settings.
9. Details are in my post. (Numbers are from "C")
bump?
Bump. On my machine it's even worse. Try to create proxies, and if you'll work with the proxies, preview will be fine. Preview set to "preview", not good or best, because then Vegas will use the original file instead of the proxy.
BTW your project is not 300p right?
What's the point of having 300p footage? Unless you want a frame perfect 1/5 slow motion in a 60p project , it's pure wasting resources.
So.. I fixed it. and honestly I don't know how.