proper backspacing for 20" Coys

[bigarmzz]

i'm def leaning towards getting some 20" coys wheels,...looking at 20X8.5 in the front and 20x10 in the rear.

for tires, i'm thinking 255-40-20 in the front and 295-40-20 in the rear.

they offer two different options for backspacing in those two size wheels,

for the 20x8.5, they offer 4 3/4 ", 5 1/4" inch
for the 20x10", they offer 5", 5 1/2" inch

i'm going 5/7 drop with shackles/flip kit rear, springs/spindles up front

what do you all recommend? stance is everything, and i dont want to mess it up by getting the wrong stuff

thanks