You can no longer perform iOS 13.3 / iPadOS 13.3 downgrade to iOS 13.2.3 / iPadOS 13.2.3. Here are the details on this.
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.
Apple has just made available to download iOS 13.2.3 and iPadOS 13.2.3 IPSW links and OTA Update for compatible iPhone, iPad and iPod touch devices. Here are the details.