Photo editing is VERY cpu intensive ... try some surface blur on photoshop and you'll see.
My point was more of less that the difference would be worth less than the $300 it costs. I imagine it would be much more noticeable with a lot of video transcoding, rendering, etc. Where the CPU is running at 100% for many minutes to hours constantly.
In my fairly basic experience with PS, I haven't come across anything that challenged my computer, so I didn't realize it could be that heavy on a machine.