Best Hard Drive Option for new MacMini

I will purchase a new Mac Mini with i7 processor for my Lightroom and Photoshop work.  My question is which is the best hard drive option given what Apple sells and what I could put together from MacSales.

Apple sells the i7 MacMini with 1T hard drive, 1T fusion drive, or 256GB SSD. Am I better off with a Fusion drive or buying the MacMini with 256G SSd and put the data on an external hard drive? My data files are getting pretty large since I bought the Nikon D800.  The advantage of buying the 256SSD from Apple and using an external hard drive are that (1) I get a 256GB SSD instead of the 128 GB SSD which is in the Fusion Drive and (2) I could get a 7200 RPM hard disk drive instead of the 5400 RPM hard disk drive that is part of the Fusion Drive. I'm not sure how important these details are for my Photoshop and Lightroom work?

There are probably an infinite number of possibilities with external drives and internal drives using the MacSales data doubler. Any advice appreciated.

David