I am not familiar with the GPU compute (or CUDA) with the nVidia Quadro k620, however, and how that helps you in CS6. The Radeon/FirePro cards are quite potent in editing/rendering in Vegas.
The big advantage of the Quadro card would be seen in "Autodesk, Maya, and 3DS Max" where the special drivers of the pro card are more advanced than those of a desktop card.
It makes a big difference in modeling, and even 2D line work.