Question on 1/2" plywood sandwich wall - <Newbie>

All:
I'm building a 4x8 benroy, and I am concerned about wall strength. My design is a sandwich wall with 1/8 luan exterior, 1/2 plywood interior with cut-outs for 1/2 inch foam insulation, and a 1/8 luan interior (i.e. no "stick" bracing). Now that I've started to cut out the excess 1/2 plywood for the insulation pockets, I'm noticing considerably more flex in the 1/2 ply than I was expecting.
My question is, once I get the insulation installed and the sandwich glued up, do you think that the wall will be structurally sound enough not to flex too much? I know everyone on TNTTT says not to overbuild, but now I'm worried about underbuild and flex! Did I goof? Should I have used a 3/4 internal ply?
Any help, consolation, or anti-hyperventilation meds greatly appreciated!
Thanks!
Spentfire
I'm building a 4x8 benroy, and I am concerned about wall strength. My design is a sandwich wall with 1/8 luan exterior, 1/2 plywood interior with cut-outs for 1/2 inch foam insulation, and a 1/8 luan interior (i.e. no "stick" bracing). Now that I've started to cut out the excess 1/2 plywood for the insulation pockets, I'm noticing considerably more flex in the 1/2 ply than I was expecting.
My question is, once I get the insulation installed and the sandwich glued up, do you think that the wall will be structurally sound enough not to flex too much? I know everyone on TNTTT says not to overbuild, but now I'm worried about underbuild and flex! Did I goof? Should I have used a 3/4 internal ply?
Any help, consolation, or anti-hyperventilation meds greatly appreciated!

Thanks!
Spentfire