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It would be 2x 2560*1600 panels of 30 inches each then 60 inch + via HDMI ...

It's on the Mini's specs page - 2 displays across all 3 ports (2xTB 1xHDMI) total. Which is assumedly exactly the same situation as you have for the thunderbolt bus on the nMP that has the HDMI port on it, except the nMP can do a single 4k display instead.
 
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