A heavier arrow will give you more penetration. With that light of an arrow your bow isn't able to transfer all of its available stored up energy, thus you are losing alot of energy. There have been a few tests done that show an arrow weight of 6.5-6.7 grains per pound of draw weight will give you the optimum amount of penetration. These studies also showed that with two arrow that weighed the exact same, the one with the higher front of center % (15%) out penetrated the one with the lower FOC% (10%)
Here is the specs for your bow with a few different weights of arrows. As you can see the 469 grain arrow produces the most energy and penetration (momentum) and this is at point blank range. At 40 yds that heavier arrow will carry its energy down range much much better than the lighter arrow will and will way way way out penetrate the lighter one. Also your bow will be much quieter and much smoother when you shoot since the heavier arrow will be able to absorb ALL of the energy transferred from your bow.
gpp= grains per pound of draw weight.
350 grain/5 gpp 420 grain/6 gpp 455 grain/6.5 gpp 469 grains/6.7 gpp
331 FPS 308 FPS 296 fps 292 FPS
85.06 KE 88.38 KE 88.43 KE 88.70 KE
0.51 Momentum 0.57 momentum 0.59 momentum 0.60 momentum