I'd just like to support the opinion of not pushing APX100 if you like what it does at your normal speed. For higher speeds, I would prefer the Neopan 1600, Ilford HP5, or Ilford Delta 3200.
With that said, if you really want to experiment with this film, then no-one should stop you. Go discover what strange effects you might get with this film at EI 800. Who knows, you may really like it! I wouldn't expect any miracles in the area of shadow detail however, but sometimes technical details like that can be incredibly boring and stand in the way of creativity.
- Thom