This one may be best for someone with more brain cells than me to confirm then. My logic was the 1/2HP is twice the power of the 1/4, the difference between the reduction is about 30% with my maths, 1 + 1 = 7 right?
70 RPM still seems a little too fast for me, but it may work just fine for you. I have the occasional issue of moving too fast and the projectile doesn't quite have enough time to fall from the feed tube into the slider or the slider to the sizing die and catches. It doesn't happen often, but something that if it ran a little slower may not occur.