Thats roughly 1210 megabytes at a theoretical max transfer speed of of 10 megabytes per second more or less. Therefore, your file transfer should take a minimum of 2 minutes, but many things can cause a network not to achieve its maximum throughput.
I guess if it finally completed it's good, but you say it does the same thing when you save the file locally? Does it stop making progress for a long time as well (i.e., did I understand you correctly)? That definitely sounds like some kind of resource problem on your computer.
Have you seen Photoshop CS6 take this long since you first installed it, or is this new behavior?
Unfortunately, I don't have much knowledge of Macintosh internals, so I'll have to defer to others on why it might be that a save operation could slow down like that. But I would check to see if the system has logged any disk failures that were recovered-from or any other errors coincident with these slowdowns you have seen.
My system is a PC, but I just saved a 1.2 GB file and did not see it stall, except it stayed at 0% for a few seconds before it starting increasing.
Might be interesting to temporarily deconfigure compression to see if it changes the behavior of your file saving. In Photoshop - Preferences - File Handling, look for the [ ] Disable Compression of PSD and PSB files setting. Also, another setting that could change the file size a good bit is the compatibility setting. Assuming a flattened preview is not required by an old version of Photoshop or another application) you could try setting your Maximize PSD and PSB Compatibility option to "Never".
-Noel
