If it were me, I wouldn't take any chances, I'd just pull the drive and let the new owner pop a new one in.
Reinstalling the OS will stop the casual person from recovering data. Secure erasing will stop everyone except professionals from recovering data. Pulling and physically destroying the hard drive stops everyone from being able to recover data.
I'm going to sell my laptop soon. I've already re-installed the operating system. Do I still need to overwrite the hard drive using something like Secure Erase? Or does reinstalling the operating system take care of that?
Thanks in advance!