Movie Marvel characters are pretty inconsistent in regards to their durability when weighed against other threats.
-Ironman in his original film copped a blast from air bombardment and fell to the ground only to rise a little worse for wear. A huge feat considering the man inside should have been shattered. Loki survived an explosive arrow that did nothing more than destroy his ship.
-Ironman hit Loki with a repulsor beam and Loki fell from the force but wasn't harmed.
-In Ironman 3
Spoiler:
He shoots an Extremis soldier in the face and the soldier falls. His healing factor kicked in after a few minutes but it showed the level of damage an Extremis soldier can take.
-Later in that film
Spoiler:
Extremis soldiers were tearing off parts of many Ironman armors with little restraint. Without needing to push their bodies to 3000 degrees like Killian was
-Loki tangled with Thor pretty well in the two films. Even getting slight moments of overpowering feats. Like the Stark Tower fight. Showing he does have the strength (although not as powerful as Thor's in the long run) to tangle with Ironman in a H2H battle.
-Ironman has the advantage of flight and ranged attacks. But a non gimped Loki can create many illusions and throw energized daggers that can kill Frost Giants instantly and has a feat of a dagger that sliced right into Thor himself. Plus Loki has the staff.
In the end Loki has shown to be non-harmed by Repulsor blasts. And strength and skill feats to tangle with Thor.
Has ranged attacks that should be able to compromise Starks armor and illusions to help him achieve such strikes.
He also has mental feats of making his victim feel overwhelmed and aggressive which should work wonders on Stark considering in IM3
Spoiler:
Stark is having massive anxiety attacks.
Loki was gimped in Avengers. He has the tools to defeat Stark whereas Tony doesn't have the tools to kill or KO Loki. Loki was still conscious after Hulk's battering (that Loki simply allowed to happen).
Loki wins this fight. Tony needs more upgrades.