There are many considerations here on vanes. It all depends on your present setup. Arrow weight to lbs your shooting for proper penetration. Forward of Center percentage on your arrow (FOC), and rest clearance.
Helical vanes or offset helps to spin the arrow for better accuracy. Somewhat like a bullet leaving a rifle barrel to speak. Straight vanes won' t give you the spin as fast, and could spin in either direction once leaving the rest. But straight gives you better rest clearances. So how much degree of offset on your vanes depends on your clearance. Latest tests have revealed left or right helical is more of a personal perference, and neither makes much of a difference. The old thinking was it depended on which hand you shoot. I hope his helps.