First thing I would want to ask you is if you have done anything with the wind buffeting you are probably getting. You shouldn't need a different radio. I have plenty of volume with mine, I am running Infinity speakers with the stock radio, no amp, And I can hear fine at 80 MPH.

 

If you don't plan on upgrading the amp, look for speakers with a high EFFICIENCY rating. The higher the speaker efficieny rating, the easier it is for your amp to drive them.
Another thing to consider is the reality of being on a motorcycle. Bike noise , road noise ,wind,etc. You may find yourself spending lots of money trying to reach a expectation that is unrealistic. I have a wicked sound system in my van.It will play louder than you can stand it and still be crystal clear. But, do 80mphand roll the windows down and you lose a lot of volume +clarity. On a bike it's way worse.

 

expensive proposition but by far the best results especially if you don't want an amp in the bags

 

I still have a inexpensive pair of JBL's that was talked about here on the forum a few months ago.....many people installed them and had very good results. I have not installed them yet. If when I do put them in, they dont perform as well as I would like, I will go with either a pair of MB Quart's and a Hawg Wired amp.....or the Hawg Wired amp, and their speakers. I refuse to keep changing crap around trying to find the best.....so I figure if I just go with the best right from the jump....it will sort of stop the bleeding early, and hopefully I will be well satisfied. For now its stock everything...with JBL speakers.....if that does the job at highway speeds, then I am done....if not.....Hawg Wired here I come. As for a antenna.....I have a lot of good things about the unit that mounts inside the batwing fairing....its shaped like a T.