[M_Six]

That'll work fine. Photo editing isn't as much about RAM as it is about the graphics card. The MBP is ok in that respect. I was rendering a large 3D object in Photoshop this week on a Mac with 16GB RAM and it never exceeded 6GB of RAM use, so 8GB should be plenty. The one thing you need to be aware of is that screen, especially if it's a Retina. Your images will look way better in LR5 on your laptop than they will online. I see that all the time with mine. Same with printing 8x10 or larger. The Retina will show your images with extreme detail that you'll lose when moving them to a lesser device.

Having said all that, RAM comes in handy if you multi-task. If you can swing a jump to 16GB RAM, go for it. The Retina equipped models can't be upgraded, so what you buy is what you're stuck with. Go big if you can afford it.