I would spend an extra couple hundred bucks and get the i7 295, if it was just LR, I would have recommended i7 290 but I think you need the power of both CPU and GPU to push that many pixels in Photoshop.
After vascillating for AGES (since it was announced really) I have decided to go pick up the base unit. I will add RAM after the fact to get to 16GB.
Justifications:
I currently use Windows 8/10, i7-3770, 16GB RAM, 256GB SSD (approx read 550MB/s and 550MB/s write with an HD 5770 attached to an Asus PB278Q (2560x1440)
The i5 is the same speed or faster in benchmarks on all that I do.
The R9 M290x is definitely better than what I have now.
1TB Fusion is my not so hot part - I currently use about 90GB of my 120GB SSD which according to Anandtech is still making great use of SSD over the HDD until you hit 2GB file size (which for me is rare)
I have a 12TB NAS w/1 free bay on my LAN.
I have no issue using TB2 to boot if I feel the 1TB Fusion is sluggish. Yes means I will need to buy an SSD enclosure.
If I do not lose performance and gain a 5K screen I will be pleased for the next 3 years at least.
Last upgrade was 2 years ago and before that was 4 years prior to that.
