With Photoshop/lightroom etc, having excess DRAM is not a drawback and higher freq DRAM is often extremely productive, if you work with these a lot (and depending on your hardware (which we don't know) I'd suggest 12 GB for a tri-channel rig (X58 based) or 16GB in 2 x8 if the mobo supports it, for a dual channel (most anything else except for X79)