Eric -
I think you called it. The main oil feeds are on the top, so the added combustion pressure is most likely settling the crank down a bit on acceleration.
The bearings are a most likely worn pretty well, but I wouldn't sweat it. Pressure's only dropping about 5 percent. It sounds like a pretty stock engine, so I'd just drive it!
When you start seeing near zero oil pressure at hot idle, that's when it's time for a rebuild.