WHO CAN BE TRUSTED?

I have both Wong and Snyder's books. snyders high lo-lite varies a lot from wongs hi-low on certain plays, such as doubling down a 10 vs a dealers 7 up card. Wong says to double when the count is greater than -6 while snyder says to double when the count is greater than -2. thats a difference of 4. i find it hard to believe that an aditional 4 tens in single deck game doesnt make a difference?????

What indices would any pros recomend?

thanks