"how can I be sure it is really wiped and is not going to fall into the hands of some spotty tech type"
What have you actually done to wipe it? The fact that it's "dead", as you say, doesn't mean it's also wiped of data.
Also, why on earth do you keep "bank, personal, work and other confidential details" on your HDD?
They should always be kept on a removable media (which is, ideally, password-protected).