what is a good shackle angle for a flexy 2 1/2" Blazer rear springs?

[CheyenneKid]

I've got some rancho prerunner springs going under my truck with a shackle flip. i haven't designed the flip brackets yet, but i'm curious about the effect of shackle angle, how it's measured, on ride and flexxx. (it'll be a porno truck, it's so extreme)

sincerely,

CK