Always wait for cleared funds from the buyer before mailing.
Need to assume the worst because the worst will happen.
You need to ship within your stated handling time, regardless of whether funds have reached you. Under EMP that may mean shipping before the funds hit your "available" balance, let alone before they hit your bank account.
You should get 2 emails on every sale. The first saying "Sale confirmed" which means the buyer has committed, but has not yet made payment. Then a second "Your item sold!" which means the buyer has made payment to eBay
and the clock starts ticking.
If you don't want to ship before actually receiving the funds in your available balance, then you need to edit all your listings and push your handling time out far enough (5-10 days) that the funds will clear before you are obligated to ship.