ahh, crystalwell. you should read this review:http://www.anandtech.com/show/6993/intel-iris-pro-5200-graphics-review-core-i74950hq-tested/2
I know that was for Iris pro 5200, but it should give you an idea of the performance of HD5000, which is: it's a big improvement over what Intel had in the past, but nothing ground breaking.
I honestly haven't seen Company of Heroes in benchmarks in a long time. given that it's a fairly dated game, you should be able to run it on medium. the games in the current benchmark sets are some of the most graphically intensive games currently on the market.
In short, I would say just about all games are playable on the new MBA (except crysis 3 lol).