I have a 6dB GME on the front of my car and it's 2.23m tall give or take the fraction of a mm difference caused by the burger that I did or didn't eat on the way home. Very useful for determining whether or not I'll be able to get into a carpark!
Be a little aware of what you're using the radio for. The shorter antenna is better in hilly terrain (city buildings count as hills as far as radio waves are concerned). The higher the gain in the antenna, the longer the reach of the antenna - but that's a horizontal reach, and it is quite polarised and inflexible. The 9dB antenna is really only good for outback travel or smacking fluoro lights like Navmania has done.