Damn.

And subtract the drag...

True. But, even if the acceleration are about the same, the gravity acting in a different way (from the acceleration point of view) makes the experience quite different. By the way, I wouldn't do a power dive with my plane. It is not airbatic, and I want to keep the wings on it for a few more years. In a power dive, it is quite easy to go past Vne (never exceed speed).

It's quite easy to get a modern sports bike to do aerobatics as well