I would concern myself primarily with how sensitive the HDTV receiving chip in the set top box is.
Otherwise, you will get no signal, or one that stutters and freezes so often that it just isn't worth watching.
The Silver Sensor is a very good hdtv antenna, it is directional so it is good in multi-path environments, but it only good if the transmitting antennas are 20 miles or so away from the set top box (the one I've got with an ATI HDTV Wonder picks up signals about 25 miles away, but reception quality depends on how powerful a signal is being transmitted - e. g. NBC is great, CBS is very tough).
If you can mount the antenna in an attic or outside, that helps a lot and Terrestrial Digital makes some nice hdtv antennas. I think Winegard Square Shooter is also supposed to be good.