Ah, you haven't seen the Trivex/poly/CR-39/1.60 comparison video where they drop a sharp (not razor pointed) projectile onto identical (except for material) lenses.
Cr-39 and 1.60 shattered, as you'd expect. Poly fared well, depressing impressively, BUT, allowed penetration of the projectile, whilst Trivex also depressed impressively, but did NOT allow penetration of the projectile.
To me, at least, that proves Trivex slightly superior in impact resistance.
http://www.youtube.com/watch?v=rKEC4zDowXs
Note the little piece of poly breaking out and flying out below the lens and to the right. After being pierced, unlike the Trivex.