This speed test video offers a side-by-side performance comparison pitting the latest version of iOS 13, iOS 13.2.3, versus iOS 12.4.1 on an iPhone 8.
Here’s iOS 12.4.1 jailbreak update. Apple is still signing iOS 12.4, which means you can downgrade from iOS 12.4.1 now for jailbreak.
Here's how to downgrade iOS 12.4.1 to iOS 12.4 for jailbreak while Apple is still signing the firmware. Here are the details.