Will update kill iPhone?!?!!?

Hello, I have an old iPhone 4 I found in a draw. Currently it's on 5.1.1, I was wondering if it's worth updating it to 6.1.

Not too worried about losing Google maps or youtube as google has released better apps. Main worry is performance. Historically Apple has always ruined older devices with newer OS versions. Anyone have experience of iOS 6 on an iPhone 4?