The pre-release description and its realization of an operational interface that sequences from notation, has me waiting for Overture 4 -- with a hope that it is well tested in Beta and solid in performance. I hope they eliminate the problems that have only been "fixed" incrementally in other programs, and my use of O3 has shown me they have the background to do it.
If you want to work with software that facillitates professional looking scores and where the majority of the input from its forum is in regards to quality engraving practices then I would suggest Finale. Finale also has excellent playback, but the other notation packages do as well, and Finale has no advantage over any other program as to quality of playback.
For me the key was to be able to enter notes as quickly and accurately as possible with as few keystrokes as possible (and no mouse at all, whenever possible). Other requirements were to be able to engrave well, export MIDI and playback MIDI. I didn't need to be able to make perfect/extreme notation for professional publication.
That was back when Sibelius 2 had just been released, and that was what I chose. I'm still happy with Sibelius' keyboard entry model (though I wish it were note-value, then duration rather than the other way around).
Anyway, if power entry is key, look into Sibelius seriously. I don't know that it's still the leader in this respect, but that was my conclusion when I bought Sib 2. (I'm now at Sib3, but haven't yet upgraded to Sib 4.)
Sibelius is great. The new version 4 introduces "dynamic parts" - where the score and parts continuously and automatically update each other, even after you have reformatted the parts. This for me will be an incredible time saver, and one that I've been wishing they could implement for years.
Finale doesn't ahve dynamic parts, yet I think that they will look into this and try to implement it next year. Parts linked to the score may be helpful to some, but could have disadvantages too, if you make major changes to a score, the formating of the part may need some polishing. Furtehrmore, if you use one staff for two instruments (flute ! and Flute 2, for example) there may be tremendous difficulty in linking a part to the proper notes, since engraving standards ask for severasl ways to display two parts in one staff depending upon the nature of the music. Even Sibelius 4 (by their own admission) would be unable to work dynamic parts in these kinds of scores.
I have mixed feelings about the utility of parts linked to scores.
Finale doesn't ahve dynamic parts, yet I think that they will look into this and try to implement it next year. Parts linked to the score may be helpful to some, but could have disadvantages too, if you make major changes to a score, the formating of the part may need some polishing.
... whereas now, if you make ANY changes to a score, you need to extract the part again from scratch and do ALL the formatting again! "Some polishing" is surely better than this?
I haven't upgraded yet so I can't say how well it works. But put it this way - you still have the facility to extract parts the old way, starting from scratch every time. Nothing's been taken away. Dynamic parts allow you to bypass a lot of that work in the situations that they are appropriate (which I think will be most).
Anyway, you're probably right that Finale will now implement the same thing pretty soon to catch up. That's how these things tend to work.