Loupe magnification is a bit loosely defined, meaning that the magnification factor is not always comparable, and not always within a brand either as in this case. The 12x has considerably stronger magnification than the 10x, not just 1.2 times.
The Silvestri 10x has got varying reviews, I have one and thinks it's okay (but 8x or so would perhaps be truer magnification), but I also know people that hate the 10x and love the 12x, so it's definitely an entirely different loupe.
The new Linhof bright screen does not have finer grain than the older standard ground glass, and I would be surprised if Arca-Swiss had coarser ground glass than Linhof's standard. So if the loupe just can focus on the grain it will be okay. I'd suggest to send a mail to Paula at Linhof Studio and ask if it will work, other customers may have tried it already.