Sorry, still not quite sure about this..... you mean a jailbroken backup can be restored to a jailbroken phone (after an upgrade ect) right?
Don't confuse "restore from backup" with "restoring the firmware". To jailbreak, you create a custom firmware and restore that firmware. When you restore from backup, you aren't updating the firmware, you're replacing all of the saved settings, data, etc from the phone. So, from the start if you're going to jailbreak, first do a full backup. Then apply the jailbroken firmware, then restore from backup and you'll have all of your email, sms, contacts, etc.
Nothwithstanding what the other poster said, I fpersonallly would stay away from QuickPwn. Its too new and there are other issues such as not getting Cydia, etc in all cases.