Can't get to my quad atm, but got a friend who took some photos of theirs to email them to me.
From memory my quad was not glossy either and I'd agree in calling it a 'satin' or 'silk' finish like you mention. The paper was quite thick, personally I wouldn't push it as far as card stock but maybe 180-220gsm (guesstimate!).
To be honest I can't remember the reverse printing that well, but when I saw my mates photos it does look like both sides were printed near enough 100%.
Front/back
'12' Mental Age
Hope that helps... can dig mine out if there's anything else that needs checking.