By this point, I'm assuming everyone's seen all the Iron Man movies, including the latest one (Iron Man 3), and also The Avengers. If you've missed any of them, stop reading now and go see it.
Still here? Good. It seems to me that most of the battles in Iron Man 3 could have been a lot easier if Tony Stark had the Mark VII, which he used against Loki and the Chitauri in The Avengers. If you've noticed, the only tactical advantage that the Mark 42 provides is the ability to deploy telepathically. It's been useful in many cases (and Pepper Potts would probably have died without it), but it's also woefully inadequate against powerful, Extremis-enhanced enemies.
The Mark VII was similar to the Mark VI (Iron Man 2) in many ways, though most functions were significantly upgraded. It had a much larger ammo capacity, for starters, and the laser cutter could also be used more than once--a culmination of all his previous efforts. The Mark 42, on the other hand, seemed to lack all of these functions--its only weaponry were the repulsors and the Unibeam.
Now, we all know Stark likes to deploy armors that haven't been extensively tested--and to great effect in many cases--but he should have stuck with the Mark VII here. Sure, it got blown up after he issued a challenge to the Mandarin, but what he should have done was put on his Mark VII (not too much of a stretch, given that he was more than a little nervous right before he was attacked) and kept all his other armors on standby, so that the Mark 42 can still be deployed to save Pepper if necessary. Given how devastating the Mark VII was against the Chitauri, the final battle would have been a breeze had Stark simply stuck to what works--its missiles could have easily killed most of the Extremis guys (they can't possibly survive being blown up). Pepper was a captive, but Stark could have infiltrated the place on foot and deployed the Mark VII when things went wrong--not like it would have mattered, since he was discovered pretty quickly. Fighting Aldrich Killian would also have been easier. Given that the final blow was dealt with a metal pipe, he probably couldn't survive be bisected from head to groin--yet that's exactly where the lasers come in. The Unibeam could also be useful here, since it's previously been proven effective against Extremis users. Instead, Stark used Marks 8-42, most of which seemed to be low-quality showroom pieces which Killian could easily cut in half (some of the armors, such as the Mark 42, could withstand more damage).
While a great proof-of-concept, the Mark 42 simply wasn't ready for combat. Its weaponry was very basic compared to the ones on the Mark VII or earlier armors (even the Mark III had a few missiles). Sure, the Mark VII was destroyed, but couldn't Stark have made another one that's equally durable and also armed to the teeth?
