OP:
If you're a Photoshop/Lightroom user, I'm wondering if you wouldn't be happier with a 27" retina model?
The 27" gives you the luxury of adding RAM later. I don't think you can do that with the 21"
Also, regarding drives:
A "fusion" drive is actually TWO drives inside: small SSD and large HDD that are "bound together" by the OS into one "virtual drive" that you see mounted on the desktop.
The point is to give the user a "faster experience" without the cost of a "straight" SSD.
I've never used one, but others report that they work well, and yield performance that is quite good.
If "money
IS an object", I would suggest this:
- get a 27" iMac, either retina or perhaps a refurbished non-retina. Get the base RAM (probably 8gb) -- you can add more later on.
- get just the 1tb HDD inside (skip the fusion and save money)
- pick up a USB3 SSD, plug that in, and set it up to be "an external booter". These are available at reasonable prices. They won't be as fast as an internally-mounted SSD or fusion drive, but they will be "fast enough".
Here's an example of what I'm talking about:
http://www.amazon.com/exec/obidos/ASIN/B00ZTRY532?tag=delt-20
A 27" model will give you the option of expansion later on.
You won't be able to do that with the 21".