Originally posted by slackercruster
As long as the 300mm prime would offer a much higher IQ than the zoom, could go for it. If the IQ is not that noticeable above the zoom...why pay the hefty premium?
The issue with lenses in these focal ranges is that resolution is at a premium.
You may not notice much difference between the DA 55-300 and the DA* 300 at web resolution (i.e., 600px), but make a 20 by 30 print and it will be blatantly obvious. Of course, you pay a lot more for that extra resolution, and if you're not making large prints or cropping, it may not be worth it.
Also keep something mind: the DA* 300 is a lot heavier than the DA 55-300. In fact, it's best used on a tripod. It's actually much easier to use on a tripod than the DA 55-300 because of the built-in tripod mount. Of course, the DA* 300 is not so heavy that it can't be hand held. And the stop+ advantage it has over the DA 55-300 can be quite significant for hand-held use (as well as IQ). But if you really want to squeeze every last drop of IQ out of the DA* 300 and get a full return on your investment, a tripod (and ballhead) is desirable.
Cropped hummingbird shot with DA* 300: