I deleted my original post and re-did the math. Here is a more correct response:
Suited 6-7-8: something less than 0.0088%. I say something less, because the proper strategy would require a player to stand on a two-card combination that could lead to a 6-7-8 hand in many cases. It would take a complex sim to figure out the proper strategy.
Triple 7's: something less than +0.0155%. Again, proper strategy would dictate standing or splitting sevens, rather than hitting to the third card, in some circumstances.