Best iOS version for iPod Touch 3G battery life (car mp3 player)?

I was wondering what the best jailbroken iOS version for the iPod Touch 3G 64gb is, in respects to battery life? I'm just using it to play mp3s in my car. It's currently running 5.0.1 jailbroken, but I was wondering if iOS4 or 3 would have better battery life? For my iPhone I noticed the 5.1 gave bettery battery life than 5.0.1, but I'd like to keep the iPod Touch jailbroken so I can use activator to enable the volume buttons as next track / previous track. Thanks in advance for any information!