To give yourself a sense of comfort with their respective capabilities, you may want to look at this thread: List Your NUC Capabilities Here
Simon Pepper and I did a comparison of an i3-based NUC vs the i7. The i3 is very, very capable. The regular Nucleus has that processor.
So, unless you have very demanding situations, or are a person who wants to feel comfortable having the most powerful version (I stand guilty), the Nucleus will probably be perfectly fine. The money you save will pay for your lifetime Roon membership! 
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