Bob, Joe...you both have me second guessing the laptop now. But I do want the convenience of being able to take my computer with me if I need to visit a client.
But. Nearly 100 percent of the time I use it as a desktop. I have a NEC 2690 wuxi attached to the laptop to do my editing on. I'd never use the laptop screen for image editing except for maybe keywording, rating, etc...
My fear, hesitation, about the imac route is reports of the screen getting discolored in areas, the possibility of it happening, due to heat from the computer parts behind it. I've read about it.
That's why I thought even closing the computer lid and attaching a second screen via the hdmi port, like an nec ea244wmi to use for palettes, browsing, email, would be a better idea. It would also be a matte screen. The big glossy screen of the imac does not appeal to me.
And for what it's worth, it seems to me that the guts of these recent macbook pro's contain powerful processors, and 16 gb of ram seems enough. Hell, I'm getting by with 6gb on my current macbook pro. Although I don't keep Lightroom and photoshop open at the same time. That can bog down my old laptop.
My hope, with 16gb of ram, would be me being able to run Lr and Photoshop at the same time. Even leave my mail program and a browser open. Still have the machine running the photo programs well. I also sometimes use Capture 1. I do ok now, even with only the 6gb or ram. I'm sure 16gb would make it sing.
I was just wondering about the need for the discrete gpu in the most expensive mbp model, the fact that it remains on all the time with external monitors attached, and its reliability. But like you mention Joe, it might make use of new abilities in Lr 6 for a lot more speed. We just don't really know yet.