I think one of the main differences between Photoshop and most games, is that Photoshop will use all the cores available to it, so as where an i7 2700k would make most sense for gaming, you can justify the i7 3930k. I am out of touch with the latest Ivy Bridge architecture.
Check out the Tom's Hard System marathon builds. This is their $2000 system: (as I said above, I don't know where the Ivy Bridge CPUs stand regards relative performance)
You need at least a Gb of video RAM, and as CS6 is making so much use of GPU, the 580GTX would work well for you, but that is a generation out of date now.
This article on Tom's Hardware might prove interesting:
It's not Photoshop, but the PPBM5 (Premiere Pro Bench Mark) gives a good comparison of systems.
You might like to stop by the Premiere Pro hardware forum:
Premiere Pro relies heavily on GPU performance, as you can see from the MPE Gain figures in the chart. Note how many of those systems are overclocked.
Photoshop will also make use of all the RAM you make available to it.
I built this earlier this year, but with Premiere Pro in mind. At the time it was fourth fastest system on the PPBM5 charts (38th now, but similar systems are at the top of the chart but much more heavily OC'd)
i7 3930K @ 4Ghz with the Intel water cooler.
32Gb RAM (the above MB has 8 slots so I was able to use the cheaper 4Gb sticks)
Full tower space (for cooling and lots of drive space)
750W Gold label PSU (the PP Hardware guys would think this marginal, but it has always coped - note that the external drives have their own PSU)
250Gb SSD for OS and program files.
2 x Velociraptor 600gb in a raid0 (project files) These are 2nd gen. the 3rd gen are lighting fast for a HDD
2 x WD 7Tb Green in raid0 (for my documents etc.)
300Gb Velociraptor just for Photoshop Scratch space.
2Tb WD Black for back up (Shadow Protect)
1Tb WD USB3 external (two off)
2Tb WD USB3 external (two off) one for another layer of backup.
Windows 7 64bit
I have never knowingly been able to max this system out (watching the CPU and memory in Task Manager while doing heavy lifting) and it has been a pleasure to use with Photoshop and Premiere Pro.
Thanks for such a thorough reply. I'll be going through each of those links and using some of that information to help my friend decide on the workstation he wants. Thanks again.
So far as Ivy Bridge vs Sandy Bridge, Ivy Bridge has focused on GPU performance and so the four CPU cores are shrunk in physical size to make room for the video. The bottom line is that overclocking is marginal with Ivy Bridge compared to Sandy Bridge due to the increased difficultly extracting heat from the chip.
That being said, if you handle the cooling correctly, Ivy Bridge will overclok better than Sandy Bridge, but for the most part, I would leave overclocking alone for a work station. I have a fair understanding and experience with overclocking i7 chips and they overclock well, but you must pay attention to all the parameters and test thoroughly under stressed conditions.
So, if you do plan to stck to stock speeds, it would be well to investigate the various chipsets available. P67 does overclocking well. H67 does not but is good for building stable systems etc.
So far as video, keep in mind that with the growth of OpenCL, more apps are using it so whatever video card you use, that is an important consideration as some filters are process intensive. I'm not sure of this but I believe that the comparable process in nVidia is Mercury, and for ATi, OpenCL.
Lots to look at and today I began my own overall look at current technology.
In general, I would agree that if a particular configuration runs Premier well, Photoshop will be a breeze. There may be some caveats here so others may chip in.