Unless you're storing all your credit card information, NASA alien secrets, or nuclear bomb plans, then what Mikuro said is great: what you've done already is sufficient.
Hackers aren't going to want recipes, family photos, your web browsing cookies, old papers from college or any of the kinds of documents people typically store on their computers. Even if they came across them, they wouldn't do them any good.
What you've done is enough... but if you suspect that there will be people expecting you to ship your hard drive and are laying in wait to steal it and forensically resurrect your data in order to use it against you for their gain, then you need to destroy your hard drive. Otherwise, ship it.