I can't believe that Archer wouldn't have something he could do to break through Gil's armour. Plus, even if he didn't, I don't see any armour on Gil's head....
Karna's armor is literally scattered bits of gold and thigh-high socks and it works on his entire body, including his head. This argument is stupid, and regardless of if it's right, do you honestly believe Gil will let EMIYA get near his face? He'd be full of swords before you can say "Surely this body was made out of swords".
As for the matchup, unless you want to perceive Gil as he seems to usually be in Mike and lantz's case (AKA A complete and total fucking idiot), he will absolutely steamroll Archer. It's just a matter of how serious you want to believe Gil is and how much plot armor you wanna give EMIYA.
Basically, for the health of this thread's future, unless you give a ridiculous advantage to his opponent (IE give EMIYA his plot armor in UBW route, Shirou his Protagonist Modifier + ONORE status effect, Let Karna get a surprise attack) and have him be entirely unserious, Gil wins against literally any human or Servant.