I wouldn't try to compare a Mac mini + Cinema Display to an iMac, as they really do not compare in terms of performance (unless you're comparing it against the base 21.5-inch Mac mini with the 1.6 GHz Intel Core i5 processor - which you definitely shouldn't consider). In respect to processing and graphics power, the iMac is really the only ideal choice if that's essential for what you do (and, as you say, longevity). It really all comes down to what you need to do with your Mac. From what you say you'll use your Mac for, a Mac mini might well be suitable. They are very capable machines for a lot less money than an iMac, and the plus side is you can swap out your monitor whenever you feel like it. However, you might want to look at the GPU you currently use and compare its general performance against the Intel Iris 5100, as this is the integrated GPU included on the upper two Mac mini models. Will this be sufficient for your graphics work? If it will be, then in terms of processing power, a mid or high range Mac mini with an SSD might well be a good fit.
You can certainly customise most Macs to include an SSD by customising it when you order it online, but most Macs come with SSDs by default, except the iMacs, where only the highest-end model comes with a Fusion Drive. The benefit of a Fusion Drive is you get similar levels of performance to an SSD, and the operating system will try to determine what files and apps you use most often and move those onto the SSD and less commonly used files and apps onto the slower hard drive. You get the benefits of the performance an SSD can provide with the storage capacity of a spinning drive. But it can never achieve the level of performance a pure SSD can deliver, but it can be close depending on how a Fusion Drive is used.
I'll break it down into what I see are the benefits and drawbacks to each option:
iMac
- Convenience of an all-in-one: it includes the computer, screen, keyboard, mouse and very good speakers
- It offers a good balance of performance to price (compared to a Mac Pro - which is really designed to be, and uses components for, workstation use cases - and is phenomenally expensive)
- Good graphics performance: you can play some pretty demanding games on the iMac models with discrete graphics (I digress; not everyone cares about that)
- Will last longer than a Mac mini before it no longer meets your requirements (however bear in mind Apple has a tendency to discontinue support for newer OS X releases for hardware older than 4 to 8 years)
- You can upgrade the RAM on the 27-inch iMacs. You can't do this on a Mac mini as the memory is soldered in place.
- If you are no longer satisfied with the screen size or if it becomes faulty out-of-warranty, what options will you have? Will it involve spending money? (However, if you live in the EU, you may still be able to claim for a repair at Apple's expense under EU consumer rights law even after Apple's warranty has ended: the exact period of 'statutory warranty' varies by member state, but will always be at least 2 years).
- Out-of-warranty repairs can be expensive on an all-in-one computer, versus out-of-warranty repairs on a Mac mini. This is partly just by nature of the size of the product, but also its design.
- iMacs (including non-5K and 5K "Retina" variants) no longer support Target Display Mode. This would allow you to use your iMac as an external monitor.
- You can only upgrade the RAM on the 27-inch iMacs. The 21.5-inch iMacs have their system memory soldered to the motherboard just like the Mac minis.
Mac mini
- Pretty good processing performance for the price. I'm happy with it, and I'm a developer for a living.
- Adequate, but not stellar, integrated graphics performance: you'll certainly get more from an iMac here.
- Much, much cheaper than an iMac. If you have your own monitor, keyboard, mouse and a set of speakers that you're happy with, a Mac mini might be a better choice if it will be sufficiently powerful for your needs.
- With an SSD, the Mac mini is deceptively quick.
- GPU performance is adequate at best, but nothing compared to an iMac with discrete graphics. The integrated GPU in the Mac minis might be suitable for many kinds of graphics work, but it's something I can't advise on as I'm not a graphics designer. Don't get the base Mac mini as that comes with a mediocre CPU and GPU combination.
- RAM is soldered to the motherboard - you cannot upgrade it after the fact. If you choose a Mac mini, make sure you get 16 GB memory if you think you'll need it later on. Be warned memory upgrades from Apple are expensive and overpriced.
Hope this helps.
