Can a hybrid bike's stem be slammed to make it nearly as fast and powerful as a road or cyclocross bike?
There is no absolute 'correct' way to get a lower more aggressive position. 

You probably can get a lower, more aggressive position on a hybrid bike by adjusting the stem angle and length, but how much lower depends on the inherent stack and reach geometry of the frame. You are also limited by flat bars which obviously do not have the drop sections that allow a very low position. Flat bars tend to be a bit wider than drop bar hoods which also compromises how aero you can get.

There is not a magic vertical distance between the seat and handlebar, so forget the 5-10cm measurement. Just experiment with what you can do on your bike, and what works for you. 

If you can get a significantly lower bar position, you may need to pull the saddle forward a little. Bikes with more upright riding positions typically have a slacker seat tube angle that puts the saddle further behind the bottom bracket.

Update added a few days later:

Be aware you are very unlikely to make your hybrid 'nearly as fast and powerful as a road or cyclocross bike'. The riding position is not the only factor. Hybrids have other design features that sacrifice speed for comfort and lower price: wider tires, lower gearing, heavier components, less stiff frames and wheels etc.