I just put Kuryakyn Sound of Chrome on my Heritage. Wired my mp3 cord thru the console and velcro'd my mp3 to the tank strip.
They're pretty decent up to about 60-65 and then they get kinda hard to hear. If it's really windy out to boot, then it's worse. If you're cruising thru town or a 50 mph twisty, they're awesome for what they are. Alot of it depends on the quality of the recording on your mp3. I have music both high and low quality. While it's easy to hide with earphones, coming thru the speakers with the engine/wind noise makes recording quality much more relevant.
But I just took my Heritage in today for it's 10,000 mile service. Mile loaner is an 09 Ultra - teal/cream.
No issues hearing that stereo at 80. :s
Oh, and I think the power output is 50 but I don't remember. There are some out there that are 100 amps, but in my view, get some decent speakers without busting your wallet. Because when you're doing 70 mph, I don't think many 3" preamp speakers are going to be anything more than just really tinny regardless of amperage. Either way, you're likely to spend about $350 to get them.
But I could be mistaken.