A 750gr (.50BMG) bullet is 5 times the weight of a 150gr bullet (.30-06). A 60% increase in case dimensions means a much, much larger volume of powder. Imagine 5 .30-06 bullets impacting at the exact same time, in a single spot. That gives you a start to figure how powerful the .50BMG is.
A .30-06 is not 60% of a .50BMG, and I don't know where anyone could come up with that idea.
A pumpkin is mostly empty space inside. Electronics are mostly thin sheets of brittle material and metal. A bullet that vaporizes a water filled jug will only leave a small hole in these things.
Under the right conditions a .50BMG could "blow up" a person, or blow off an arm or leg, just as a .22-250 will blowup a small varmint. However, most of the time, the big .50 is through and gone before that much energy is dumped in a soft target. Since .50BMG bullets are not designed like varmint bullets, "blowing up" a person (or a part of one) is a very rare event.
All else being equal (and it almost never is) bigger bullets tend to work better.