Hey Tim,
I usually run around 6.5 to 7" on the 64".
Don't have one that I'm shootin this year,but measured last years 62"(same form) and it is 7 1/8" brace.
The 60" experiment I'm shootin this year ,I just measured at(hmmmm)7 1/8" also.
I suppose a lot of factors figure into the BH,like shooting style,arrow weight and who knows what else!
GF Asbell wrote one time,start low and raise bit by bit,when it quietens noticeably ,that is the sweet spot.
I'd have to kinda agree with that.