NVIDIA GeForce GTX 680 2 GB & Photoshop CS6

I am planning on getting a new Mac Pro in January. I have four questions.

1) What is your experience using a NVIDIA GeForce GTX 680 2 GB on a Mac Pro (preferably 2012) with Photoshop CS6?

2) I have read that two of these cards together yield even better results in PS CS6. Is that true?

3) I have read that having two different graphics cards causes problems in PS CS6. Is that true?

4) I will be getting a 27" Eizo Coloredge monitor to use. Has anybody connected the GTX 680 to an Eizo Coloredge monitor via the display port? Any problems?

Background:
I am planning on getting a 3.3 GHz 6-core Mac Pro and putting in 32GB of RAM (possibly 48GB) and two SSDs (probably 480-512 GB each) (i'll use one for my software and OS and the other will be a scratch disk). I will also put in multiple ports for esata and USB3, as I have many external hard drives for digital asset management.

I work with large files (right now up to 3GB per image) and am limping along. I have upcoming work for files of 6GB or more per image, and I want the fastest possible system that can work with my Eizo monitor and multiple external hard drives.

Thanks for your help,

David