Are there good jailbreak apps that will improve the performance of iPhone 3G? I've an old iPhone 3G that I want to give it to my girl. She don't need it for play big games or stuff like that, but it's really slow in most of common tasks (access contacts, email, etc).

And since she isn't going to use many things the iPhone have, I was thinking in jailbreak it to see if there are apps that let you strip some of these things she wouldn't use.

Do you know jailbreak apps that strip functionality/features to iPhone 3G?

Or it'll going to be slower than now?

EDIT:
I expect something like remove unused characteristics like folders, or any stuff that make it slower. Kinda downgrading to 3.x but having compatibility with new apps.
Since overclocking is not safe for the phone (due to heat and functionality) I prefer to not consider it as an option, but thank you guys that suggested it!
Not a jailbreak solution, but... turn off SpotLight.

Go to Settings > General > Home > Search Results, and turn everything off.

This should result in a noticable speedup.