4W vs 5W - negligible difference if any at all. Performance difference will come out of receiver and transmitter details, that I can't comment on because did not see schematics, tests, etc. Antenna is removable. Actually, they are interchangeable between 3170 and 3180. There are two types I own and I prefer longer antenna (KRA-27) on my 3170. And 3170 is not that much smaller than 3180. Maybe inch and a half shorter. If you already have a setup for 3180, cables and other accessories, it's not worth to move to 3170 in my opinion. Being it fat bulky in-your-face radio may be a positive. To one crowd you may look like a cop, to another like a vigilante militiaman. Exploit possibilities!