Hey, I'm kinda in the same position and asked around for this. I'm used to 17" screen right now and been able to play around with a cMBP 15" and 17" to 15" ain't that bad.
For your case, using photoshop a lot, I think it's better to go for the 15" rMBP. The great screen, big resolution and good graphical processor is a thumbs up for the rMBP I think.
I'm buying a new rMBP next month myself so till then (quite long ) I can't say how it is.