Oddly enough, I suspect it isn't 5x speed gains over the 2012 quad model.
Sigh... for all you doubters, there is always... I repeat, ALWAYS, going to be an Apple tax. There was when the 2012 released, and the upgrades when new to i7 2.6ghz and 16GB RAM were available. No one was gonna pay Apple's storage and RAM prices then, and no one is going to pay them now.
Today, we can still upgrade RAM with other solutions... and storage this day and age just happens to be via TB3 or USB 3.0. This is the Mac mini we were all wishing for... and now 50% of forum members complain about the price. Keep in mind, this may NOT have happened at all... but Apple delivered anyway.
... just think about it for a minute... they made it with a 6 core processor, and a multitude of ports. You can expand indefinitely. This is essentially the 2013 Mac Pro at nearly 1/4 of the cost... can you really complain just because of the Apple tax (which always existed)?