Third model? Holy crap. I wish I painted my third model that well. It took me an entire army to figure out painting.
If you want to make it in a GD, here are 6 things I'd suggest:
1. No metallic paint, only NMM. If you are going to use metallic paint, use it in small areas and highlight/shade it very well.
2. Smoother blending of colors to get a softer transition.
3. Freehand work (banners, scroll work, etc).
4. Dynamic positioning. Don't just put the model together; make its stance give the feeling of action.
5. Custom sculpting and converting. Add addittional things to the model. (purity seals, extra bits of armor, alternative weapons than the normally accepted ideas).
6. Dynamic theme. Pick a good theme to convey with your entry.