The 5'10 board seems way better for you in terms of catching waves and gaining confidence.The 6'0 at 19 may make the learning curve a little tougher and you may get more frustrated at the speed of the board and the more difficult transition. The Sashimi should be ridden 2 to 4 inches smaller than your typical shortboard and its good for small wave riding.
It seems like you have a lot of opportunities to surf (3-5x's a week) and to me the ability to get out there consistently and pay your dues will lead to ur success. I like CI Boards, however, nothing compares to a FIREWIRE in my mind. I have about 12 boards in my quiver and it blows them away.