You'll always hit a hard total of 8.
Chances, as always, are good that you'll receive a ten if you hit, which will give you a respectable total of eighteen. It's also impossible for you to go bust with this hand.
You wouldn't double down with an 8 because even if you do get dealt your hand, it's not strong enough to want more money on it, because there is still a good enough chance for the dealer to beat you to make that unprofitable.