Quadro 4000 and Premiere Pro 5.5

I have recently installed a Quadro 4000 card on my Mac Pro (please refer to specs below). The card was professionally installed by and authorized Apple technician.

I have been editing H264 Quicktime file from my Canon 1D mark 4, with Premiere Pro 5.5 and have been experiencing “chugging” when I play back the timeline - is this normal??

Before the card I would transcode the H264 QT’s to max. motion JPG and proxy files (using the proxy files for editing) with Red Giant Grinder. I was hoping the Quadro 4000 would eliminate the H264 transcoding process on smaller jobs.

Mac Pro - OS 10.6.8
Quad Core Intel Xeon 2.4
16G Ram

Please see attachment for card setup information.