l_v
How are you clipping footage away....using the scissors tab on the stem of the Timeline Indicator or other?
I think that the next best step is to go for your export and gauge the performance at that stage.
Then we can evaluate the performance of the overall project, importing, editing, and exporting.
ATR
Add On...Have you gone through the usual troubleshooting drill of deleting the Adobe Premiere Elements Prefs file?
For Premiere Elements Mac, I believe it should be found...
Users/User Name/Libraries/Application Support/Adobe/Premiere Elements/11.0
and in the 11.0 Folder should be the Adobe Premiere Elements Prefs found to be deleted.