i have a 4 year old iMac and 2 year old 13 inch rMBP. When I use Lightroom, I tend to prefer to use my MBP but the gpu isn't quite up for the job and I can use a faster cpu, although I like the portability of notebooks. Should I get a new iMac with upgraded hardware or a 15 inch MBP with faster gpu? I know I can get a better performance for cheaper with iMac but also like the portability of MBP. I want to hear how others deal with this question.