So I bought a new i5 iMac with fusion drive for an employee thinking it would have sufficient performance. I upgraded the ram to 24gb.
She was let go about a week ago and I've been using the machine myself since, its underpowered for our creative needs and it's clear to me that I should have gotten the i7 chip with SSD now.
Is my only option to sell the machine and buy a new one with the specs I need? If so, what would be the best venue to sell a 2 month old Retina 5k iMac? Craigsist, eBay?
You've left out three key pieces of information needed to give you a proper answer.
1. When and where you bought the iMac
If you bought it from Apple in the United States they have a 14 day no questions asked return policy from the day you received it as long as you kept the box and everything else that came with it (see the link below)
http://www.apple.com/shop/help/returns_refund
If you bought it somewhere else, check their return policy. Many big box electronics retailers like Best Buy have 15-30 day return policies with no penalty even for open items (again assuming you have everything and its still in good condition)
Assuming not a lot of time has passed, just return it if you can.
2. Exactly what model you bought (please include detailed specs) ?
From what you've said I'm going to assume you bought the stock mid range model with the 3.2Ghz i5, 1TB "Fusion drive", and M390 GPU.
3. In what way exactly is the machine "underpowered for your creative needs."
Depending on what you mean, you may not be best served by just rushing out to buy another RiMac. What kind of applications are you running? In what way is the performance inadequate and by how much? While it doesn't sound like its a ram problem, from the scant description you provided it could be anything from the CPU, GPU, or storage system to just plain old poorly optimized software.
For example, if the CPU/GPU is the problem, even BTOing the 4Ghz CPU/M395X GPU from Apple only gets you so much more performance. If its really THAT inadequate you may need to be looking at something like a Mac Pro (although I'd recommend waiting for the next refresh).
If on the other hand all you really need is an SSD boot drive/ more SSD storage, a USB 3 or Thunderbolt attached SSD should work just fine (assuming you don't need the PCIe speeds of the Apple SSD).
Of course, if you're software is just poorly optimized then its going to be (relatively) slow no matter how much hardware you throw at it, so in that case I'd advise evaluating other software options.
If for some reason you absolutely MUST sell it, I'd advise that you first attempt to sell to someone you actually know, or perhaps another business in the area. You may need to offer them a bit of a discount to sweeten the deal, but its you'll save a lot of hassle vs trying to sell something that large on Craigslist, and a lot of money compared to selling on eBay with their ridiculous fees. If that's not an option, well I'd recommend just paying the eBay tax and getting it over with ASAP vs getting jerked around on CL.
