It's not a good idea to rely on Factory Recovery to reinstall the OS when you tire of its performance. Instead save that in case Windows 7 ever becomes irreparable.
For less urgent performance issues, get to know the Windows 7 System resources, logs, tests and fixes so you can monitor and heal problems yourself: troubleshooting steps
Many performance issues can be solved by Cleaning up factory bloatware
to enjoy Windows 7's native feather-light, instantaneous performance.
Most tech enthusiasts clean reinstall just the OS using the Product Key on COA sticker, which Dells makes easier by being one of the few who provide a Reinstallation DVD: Reinstalling Windows 7
Once you've done this then the modern way to Reinstall or Recover if Windows 7 if it really needs it is to use the built-in drive imaging to reimage the HD from a stored backup image in 20 minutes: Backup Complete Computer - Create an Image Backup System Image Recovery