A couple of comments -
John's right about not letting people tinker with radios without real alignment equipment. With voice radios you're looking for modulation, not just signal strength. You want to maximize the undistorted modulation. That will get you much farther than large increases in output power. Output power increases by people who don't quite know what they're doing often accomplish nothing more than generating higher amplitude unmodulated carrier.
I also understand his reasoning behind wanting a large whip antenna although I've never used one myself.
Remember, it's not just the impedence match you're looking for with an antenna but you want it to be an effective radiator. Antenna length is likely to give you that if the system is designed correctly. There's no real replacement for lots of aluminum in the air.
A friend and I used to talk all the time on 10 meters across town using only dummy loads for antennas. Great match, but not much for propagation. Enough to get 15 blocks with 100 watts though.
Thats an extreme example of a great match and a poor radiator but you get the idea.
Brian is right to point out the coax velocity factors. Keep in mind it's different for every coax type. I never bought into the 18' coax length but that's because I've not used antennas that aren't really tunable like the typical 102" whip. On those antennas you have limited adjustability so since the feedline is really a part of the antenna system, it's useful to have a coax length that gets you close to a correct impedance match on a typical installation.
Me, for a CB I've got an old Cobra 146 SSB rig with a lighter adapter and some no name mag mount for the car. I use it on trips when I know I'm going to be with people who also have CB's and don't bother with it the rest of the time. I did use it in the house with a base antenna for a while and have worked both coasts with it on sideband. But that's easy on 11 meters when the band's open...
jsharp - KE9JR - extra class amateur.
