Lots of factors for penetration, but here's some really straight forward "math-for-fun"...

Don't have your numbers for speed, but I played with different arrow weights with one of my bows last year, had a very similar experience. As an engineer, I started asking questions, then recalled that PENETRATION IS ABOUT MOMENTUM!!!

So here's how my bow shook out, KE was just about flatline no matter what my arrow weight is, makes the math easy, at that time was 88-89ft.lbs. 383grn arrows were 323fps, 420grners were 310fps, 350's were 335fps.

So yeah, the 335fps with the 350grn arrows seemed REALLY cool. BUT: Newton's Law for conservation of MOMENTUM is what is important, not kinetic energy.

The 350grn arrow at 335 is 16.9lb.ft./sec, the 420grn arrow was 18.5lb.ft./sec, about 10% more push-through-the-shoulder power.