If you disable video preview in After Effects to the Matrox device, does RAM preview run in real time?
In After Effects CS6: Preferences > Video Preview, set Output Device to Computer Monitor Only. Matrox devices may also require you to disable WYSIWYG preview in their control panel.
When video preview is enabled, every frame is transcoded on the fly at display time to the format (dimensions, PAR, frame rate) requested by the device. This requires some memory and processor power and has an impact on performance. If having video preview enabled is in fact contributing to the issue, you can reduce the memory requirements of the frame (and therefore the processing power required) by reducing the RAM preview frame rate or resolution values in the Preview panel, reduce the project color depth, or disable color management in the Project Settings.
Worth noting here that After Effects CC 2014 (13.0) uses Mercury Transmit for video preview, instead of the older QuickTime and DirectShow technologies, and while it is still subject to the limitations above it provides better performance.