I'm looking to get a new 15" rMBP (moving from a mid 2011 Air) and am up to deciding which i7 chipset to get. The most taxing use for me is Lightroom 5 for huge RAW images (from a Nikon D800). Other than 1 "active" Catalog at a time, I will use external HDD for image storage, so internal Flash can remain at the base 256Gig. I understand that Lightroom is CPU/ memory "hungry" and I do not need the dGPU version of the rMBP 15". However, I really do not know which i7 (2.2 vs 2.5 vs 2.8) would be the "best" for my needs? While I would strongly prefer, for travel weight/size reasons, to stay with an Air or rMBP 13", I'm thinking this 15" will remain my main/ only computer, and I plan on an external monitor in the future. Thank you in advance for any suggestions/ advice/ data-points.