Greetings.
I, too, am investigating OS X screen-casting software with the capabilities you outlined. Personally, for this genre of software I believe it is best to go with commercial software. Thus far, the 'big two' ones I see for OS X are ScreenFlow and Camatasia.
If I do not locate any other major players for screen-casting software, then I will elect to purchase ScreenFlow. Here are the criteria I elected to measure my decision:
1. ScreenFlow appears more intuitive to use than does Camtasia.
2. ScreenFlow does not require a Quark Extreme-compliant video card/engine (not sure if it's an actual piece of hardware or if it is a graphics rendering engine); Camtasia does require this. I contacted both companies and Camtasia's company replied that my system will not support Camtasia. ScreenFlow's company responded that my system is more than enough to support ScreenFlow. I placed a follow-up question to the ScreenFlow company asking for further clarification, for which I await a reply. Namely, how will will ScreenFlow perform when using an external Apple 30" monitor via Thunderbolt. FYI, here are the relevant specs on my system:
MacBookPro
2.7 GHz Intel Core i7
16 GB 1600 MHz DDR3
NVIDIA GeForce GT 650M 1024 MB graphics
Camtasia offers more in the way of video effects editing, and it has the advantage of resizing the various audio and video timeline lanes more flexibly than ScreenFlow. Personally, these capabilities are a bit overkill to me for producing quality screen-casts. If I want a more 'polished' video production feel, then I would take my rendered screen-casts and embellish them in video editing software (e.g., Final Cut Pro).