I am 6ft, and rode a 21″ frame with a slack 74 degree head angle for most of my time bmxing (having tried different combos of both head angle and top tube length). Combined with some 29″ bars with a 8.5″ rise the bike felt like a limo, but was so stable at high speeds and when airing about the place.
This was the frame I used to ride, and that I still have in my loft: FMB Steadfast
So, for your height, ideally look at 21″ or at least nothing below 20.75″. Anything shorter will be too cramped, unless you are a planning on doing a lot of slow techy street riding.
As for head angle, I would suggest a 74 degree, as 75 degrees is very twitchy, and will have a lot of pop in the front end (i.e. falling of the back a lot of the time).
These recommendations come from a park background by the way. I guess BMX race will be even slacker, and longer!