Step Up Board Concave- Single or Single to Double?

Hey everybody, making a step up board for the Fall.  Board will be designed for those overhead NW/SW Cali combos.  OH++ Beach Break, and California reef break conditions.  A 63 (8 inches longer than my normal board) & Tri Fin set up.  Foam++ for paddling, moderate rails, rounded tail.  I want a good cross between a gun, and a larger version of my regular board (standard shorty 510).  Debating over the concave.  What say you!?

Thanks.