Seeing as it hasn't really been discussed yet, but you asked, both radios in stock form have the same power. Assuming you run the same antenna they will have identical range. All radios are limited in their power output by the FCC.
It is true you can "tune" the 29 to put out more power, but it is illegal. However, I've never heard of anyone ever actually getting in trouble for it and basically every trucker has theirs tuned, but it doesn't change the fact that it is illegal. The 75 can't be tuned in the same manner.
Besides the radio, everything else is the same. You would mount the antenna and everything in the same manner. I'd recommend a Wilson Flex antenna because they are good antennas with the ability to flex as the name implies. No springs needed. Even with a spring mount, I've still broken antennas before. Also, pretty much every name brand antenna is tunable. Many people don't tune them for whatever reason, but consider it a requirement to do so. Your CB will work far better and you won't piss off others on the trails.
Regarding "tuning" a CB to push more power, it's kind of a waste unless everyone else you wheel with has theirs modded too. You have the ability with more power to send your signal a greater range so more people can hear you, but if theirs is stock, you can't hear them so what's the point? With a tuned (antenna tuned, not modded) 75, I can generally get a good mile of range with other tuned CBs in the woods in semi-hilly terrain. On the highway on flat ground, I can go much further. If you really want or need more range than that then go HAM as it's far better, and with a large repeater network that can pretty much allow you to talk wherever you need. "Tuned" CBs is just annoying when you hear some guy who is blowing everyone else out because he has more power and can't hear others talking.
As for your choice of CBs, pick whatever one fits your needs with options and mounting choices.
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Last edited by oz97tj; 09-26-2011 at 10:17 AM.