Server Load vs vBulletin

I currently run vBulletin 4.x and I was wondering if I migrated if it would be a larger server load than what vBulletin produces? If so by how much more strain would it cause the server? I run a VPS, but I do have other clients hosted on it.

It’s impossible to predict load without any information such as number of users, topics and such. My gut feeling is Discourse has steeper system requirements than vBulletin though. However, you can run it on very cheap digital ocean servers if you are cost conscious.