Photoshop use more core, so you go for i7. If you consider AMD then go for latest piledriver based 8 core FX 8350 or 6 core Phenom II X6 1100t BE
i5 will be fine.. photoshop isnt very intensive.. if anything you will have to wait a seccond or two for it to apply filters..
I'm pretty sure Photoshop's biggest performance factor is RAM, not processor. I've used even a Pentium (4 or equivalent?) with Photoshop CS6 and it ran perfectly, but even 4GB of RAM gave me issues when working with high-resolution files.