It can't be that you can't restore your most recent iOS backup which was belonging to your iPhone 4 into an old iPhone (say iPhone 3Gs). This should be possible, or at least what I know for certain is that I can restore my iPhone 4s recent backup into my iPhone 4 without worries, iTunes doesn't show up old backup available for the iPhone 4. Plus unless I'm missing out something, if you have made numerous backup on your iTunes, how comes there is still a 2010 backup in your iTunes? iTunes can only hold into its backup directory 5 backup, not more than that, doesn't matter what version of iPhones you are backing up into iTunes or how many iPhones you are connecting to iTunes. In your computer, go to User> User name> AppData> Roaming>Apple Computer> Mobile Sync> Backup/ and check out how many files you have there. Alternatively, you have the option to pull down the dialogue box of backup restore to chose from the available backup files. It will be surprising to know that you can't restore a newer iPhone backup files into an older iPhone. This is not the case of iPhone 4s backup files restoring to iPhone 4 anyway.