well, sustanon 250 if actual sustanon is
1 milliliter of Sustanon 250 Contains:
30 mgs Testosterone Propionate
60mgs testosterone Phenylpropionate
60mgs testosterone Isocaproate
100mgs testosterone Decanoate
so by dosing 2x a week, you are effectively sort of wasting the propionate to some extent and causing more overall level fluctionations as its halflife is the shortest, sometime between 1.5-3 days (partially dependent on injection site as well).
Still its pretty common to dose it that way. Every other day would be optimal, which ends up at 3.5 doses per week, so to hit 500 you'd want somewhere between .5 + .6ml EOD for best results.