Also, does the fact that the IW beat an army that was 200 points OTT mean that they are slightly overpowered?

Not at all. The IW leaders just demonstrated their usual superior tactical skill, keen judgement, iron will, and decisiveness.

We also had (almost) average dice luck, which is way above our usual.
The Iron Warriors list was not suppose to be seen in any tournament, just a fun and friendly game. In our last game, the IH had faced a mainly Infantry force and Trent had wondered how his IH would fare against an armoured one. That led me to make an army with as many tanks as possible, 53. I'd have had even more, but I feared IH airpower so had to lose a few to get fighters.
IMHO this IW army is not a very viable one. The firepower is great, but as Trent so ably displayed, assault troops could cut them to ribbons. More IW infantry was needed. The IH is a good army, but I'm not sure an army very heavy in Dreadnoughts is any better than one of tanks. I prefer a good mix of all arms .
I'm not too worried by the inequality of points. I've accidently done the same thing. Besides, when I play against Biel-Tan, Greg's usually blown away 300 to 500 points of mine before I make my first move.
It was a very good game, with our usual mixture of laughter, despair, disbelief, and head slapping moments. In short, lots of fun.
Britt