[DEcosse]

....The reason I am in doubt is to save a few bucks. But also because I have a thing where I buy hardware way to powerful for what I actually need, because I get "greedy" and think "for just a little more, I get a better CPU", but if you take a little more, a lot of times, it adds up ;-)

I'm aligned with you on the 'for just a few dollars more ......' but then 'it all adds up'.
That is exactly why I used the Linux solutions - even with the i5, I still was about $75 less than would have been with i3 and Windows 8.1.
Truth be told I probably did not need the i5 either - but by eliminating the Windows OS, put the savings into the higher spec hardware
(you never know what is around the corner so having the higher specs can't hurt)
And once I recover from the initial cost outlay I am committed to put the rest of the savings into donations for these fine developers - not least, this great team at XBMC!
I just bought the XBMC TEE but plan to contribute more.
(Much rather give them the money than Microsoft!!)

.... I tried Ubuntu with (I think it was called) Moonlight, which also should be able to run Silverlight, but I couldn't make it work, why I haven't really considered it.

Moonlight was intended to be a Silverlight replacement plug-in, as opposed to Pipelight, which is a conduit allowing Silverlight to run.
Pipelight definitely works.
Also, Linux Mint is Ubuntu based - but the User Interface (desktop) is much more user friendly than Unity.
As I suggest, spend a little while trying out the combo on a 'live' Mint stick and see how it works for you before you make a final decision.