Not sure how to help with performance issues but I can suggest a test.
Import your seq image files into a suitable After Effects comp eg match the dimension / setting of the PremPro Project in the AEFX Comp
Export an avi or a mov and re import it into PPRO as clip.
PS this is a workflow I use all the time when dealing with animations. I never bring the seq image files into PPRO becaue its too messy and un mangeable..