You might be at the disadvantage using Premiere Elements 9.0/9.0.1 Mac as a 32 bit application and the high resource demanding AVCHD format for editing.
Premiere Elements (Windows) is a 32 bit application whether run on 32 bit or 64 bit computer. In the case where the Windows computer is 64 bit, version 9.0/9.0.1
is running in the 32 bit compatibility mode of the 64 bit system, with max supported RAM = 4 GB. I am strictly an Elements Windows user. I have read about
32 bit and 64 bit kernels in Mac. The Mac 32 bit kernel may be able to use more RAM in this type of situation. Not sure, but something to explore before considering moving to the latest version of Premiere Elements.
On Windows, Premiere Elements is a 64 bit application (with all the resource implications that come with that) only when it is run on Windows 7, 8, or 8.1 64 bit computer.
It is my recollection that Premiere Elements 11 was the first Mac version that Adobe offered as a 64 bit application in a Mac 64 bit system.
Relating to the above, I would suggest that you evaluate your Mac operation with regard to just how much installed RAM is available to your Premiere Elements 9.0/9.0.1 Mac project.
The typical workflow starts with you selecting a project preset that matchs the properties of your source media. Export settings consistent with the project settings are expected to give the best results. If you are not running Premiere Elements 9 Mac as the 9.0.1 Update, then I would suggest that you do so.
And, no multitasking while working with your Premiere Elements project.
Let us start here, compare Mac and Windows notes, and then decide what next.