This is so old that nobody's likely still watching it, but...
Very often an 8 bay antenna is two 4 bay antennas. If that's the case, the difference between them is that the 8 bay will give you more signal strength and slightly more directional reception. If they are of different construction, it's a bit harder to tell.
These aren't usually considered long range antennas, though.
People are usually better at giving focused answers than at answering questions as general as yours. Can you pin things down a bit? Are you fifty miles from the broadcast towers? Are they all in the same direction from you? What is YOUR situation that you're trying to improve?
