Both Quadros are not worth their price. They are underspecced, underpowered and overpriced. It you compare them with the GTX line they are two generations old, and their price is nearly 4 times higher than the comparable GTX card. For instance, the GTX 460 for € 160, basically the same card with the moniker Quadro 4000 for € 750.
Yes you are correct after further research the GT 570 has 480 CUDAs and the Quadro 4000 has only 256 CUDAs. Are there any other factors? Does the bit rate of 8 bits for the GTXs as opposed to the 10 Bit rate of the Quadros a major difference besides the colors of 400million as opposed to 800 million?
Only if you have a HP Dreamcolor or similar monitor and use 10 bit source material, but the number of people than spend more than € 2200 on a 24" monitor, would then probably opt for a Quardo 5000/6000.