I own the elusive Shu ME Silver 945 + all the subsequent relaunches of this colour in the Shu line... none of them are exact but definitely passable especially once they're on your eyes. Back of hand swatches can highlight minute difference in colour, but what makes the ME Silver 945 superior is the texture and finish. The original Shu ME 945 has a BUTTERY texture that is unmatched in any e/s I own. I pulled out the dupes mentioned and the original, and this is what I see in differences:
ME brown 850 is more silvery and slightly lighter
ME medium brown 856 (new Atelier) is more brown and sheer
Majolica Majorca SV821 slightly more purple
I'd say out of these, ME brown 850 is the closest in colour, but this shade is also now discontinued... so not the ideal substitute. I'm not a huge fan of the new Atelier e/s as they're not representative of the amazing quality e/s that Shu is known for - the pigmentation is lacking and the staying power is poor. I'd say give the Majolica Majorca one a try since it's less expensive and it's a pigmented, good quality e/s.