I'm looking for a high-impact voice, but I don't want shouting. The voice should display a sense of drive and determination. 

You'll need a professional setup. Popper-stopper is a must, and no hard surfaces behind you. If you haven't a popper stopper, you can make one with a coat hanger and a pair of stockings. To avoid hard surfaces, you could record in front of an open wardrobe with hanging clothes. This minimises the reverberant room sound. Thank you and good luck.