I work with large 35MB RAW images from a 5D Mark III in my regular workflow. One of the big things that photographers need is SSD throughput. As you know if you have a large library, you have to store it externally. If you store it on a standard non-raid non-sad array that will be a HUGE bottleneck when viewing images in LR/Aperture. So just know what your needs are because they are different for different parts of the workflow and you should budget accordingly.
Viewing and minor editing without lag in LR/Aperture: Need external raid array or large amount of ssds
Editing in photoshop: Above + high amount of memory (16gb minimum) + processor speed (Aperture requires decent GPU)
So which would be the best GPU? Iris Pro or 750M driving an external monitor?