Meh, silver isn't that bad.
Totally depends on the class too, on a Geth wave a level 4 Quarian infiltrator would probably be ok (I reset my infiltrator and ran either a Silver or Gold immediately, scored quite low but focused on staying alive, hacking the right targets and stealth ressing ^.^)
Seen some really odd things too though, like that level 20 engy that only got assist medals... when 80% of the waves were clustered around my decoy and the rest were being killed to the left by the sentinel :s
And yeah, only run public atm, think the endings annoyed a few people I ran demo MP with/they haven't got it yet