You have to think about the context in which you're using a high-end video card.
If you're playing a video game (looking for high 3D frame-rates), then absolutely a high-end video card will aid performance.
For DAW purposes, where we're not pushing graphics hard at all... a high-end video card will
not increase performance. You'll not be able to run additional plugins or work at lower audio latency.
- If you want to run four large displays, a higher-end video card will be necessary.
- If you do a significant amount of video editing/rendering, a higher-end video card is recommended (aids video processing/rendering). Some video plugins (ie: New Blue Titler Pro) won't operate without a higher-end dedicated video card