I’m posting this admittedly subjective response because I have experience with both nVidia’s Quadro series and GeForce display adapters. I still use each computer and have noted the comparative differences in performance between the two.
The Quadro 3000M is in a Dell Precision M6600 mobile workstation, which is a very powerful and fast system. A GeForce 840M is the display card associated with the other system, a Dell Inspiron 17. The GeForce is integrated with an Intel HD5500 to equip the system with an integrated display adapter.
The description of the latter system makes it appear to be the more productive computer, however I have observed that the performance of the system with the Quadro 3000M is noticeably faster in responding to file saves and it seems to handle large files more successfully than does the newer Inspiron system.
I use SketchUp extensively and several recent models have approached or exceeded 100 mb in size, in spite of my using frequent purge actions and knowing how to model using groups and components to minimize model size,. I have found that the larger files often result in a “Not Responding” dialog when opening is attempted on the Inspiron while the M6600 opens them after a 10 to 20 second delay. In fairness to the Inspiron, the files do eventually open, but the wait is frequently interminably long.
There is no noticeable difference in graphic resolution or the appearance of colors/visual images so no preference is offered on that account, however, if I were to choose one or the other based on my experience, I would tend to favor the Quadro series even at an increased price point.