I have just replaced my 3.06 GHz Core 2 Duo iMac, with 8 GB RAM and a 1 TB hard drive, with a 2014 2.6 GHz i5 mini, with 16 GB RAM and a 256 GB SSD. Blackmagic Disk Speed tests indicate that both read and write speeds are about seven times faster on the mini.
Don't be fooled by that article. All it makes visible is that Gimp is crappy software that does not use the i7 8 threads.
New mini's don't come with 8 threads no longer though
If you can find an old 2.3 quad, then put in a 256GB SSD yourself in the empty slot, and you have a monster compared to your current machine.