Frequency rates
Stanford Wong's Professional Blackjack contains the frequency rates for various levels of the hi-lo count. In his benchmark 6-deck game, the frequency rate for counts of +2 or greater is 16.88% of the time. This is a game that is penetrated to 5 decks. The rates will vary based on penetration. Blackjack Attack has frequency rates for a variety of games and levels of penetration in its famous Chapter 10. You will find the frequency rate for counts of +2 and above for a poorly-penetrated 6-deck game (4 decks of penetration) is around 13.25%.