I'd go quad core
Reasons..
1, multipul transcodes add up
2, quad core will get things done quicker
3, whilst transcoding it won't be maxed out and should be quieter
4, system longevity
one big reason to go quad core is quad core has fusion as an option.
so if an ssd is added by a certified tech in a quad your warranty should be good.
First off, I am an Apple Certified Tech...secondly, I work at an AASP and have at multiple AASPs. Thirdly, while an Apple Certified Tech CAN install a third party drive into a machine in which the drive is not considered a user-replaceable part, YOU ARE NOT SUPPOSED TO! Read: Apple doesn't want us doing that. If Apple gets wind of us doing that, we can lose our AASP status which would be bad seeing as Apple is no longer taking applications to become an AASP in the US.
Functionally, this means that any Apple Store Genius Bar guy can look at your machine, see that an aftermarket drive was installed and deny service (as an Apple Certified Tech would not install an aftermarket drive they are not supposed to for in-warranty machines). It'd be a dick move on their part, but according to the warranty agreement, they'd be well within their rights. Same exact thing goes for the AASPs. Trust me on this.
yep so the quad needs a 128gb ssd from samsung added be a cert tech to be a warranty serviceable fusion.
you can't turn the dual into a fusion without voiding warranty.
( setting back to stock can be done but it is not legal if you are doing it to collect a warranty)
BTW this is why buying refurbs have an advantage as they don't always come with oem parts.
So if you want to crack open a mac mini you are better off with a refurb.
I have purchased 200 refurb minis maybe 5 or so had much better parts then specced. Non oem ram and even an few non apple hdds.
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My own opinion is Apple should offer easy hdd access for consumer diy upgrades. Since they don't they should offer much more choice.
Well Apple does neither and non authorized DIY is the best way to build a far better mac.
(been true for a long time)
If you want to argue that Apple is wrong to sell fusion with a 128gb ssd option and not a 256gb/512gb ssd option
(forget high pricing just more choices)
In moral court I would vote for you. But in a court of law good luck.