Don't Upgrade To Unity 4.3 Yet
Drash and I both ran into the same issue after upgrading to Unity 4.3. The game runs fine in the editor, but when it is built it runs very slowly. This isn't specific to Rift projects either. I get the issue even on the AngryBots example project. I posted on the Unity forums and hopefully someone can find a solution (http://forum.unity3d.com/threads/210543-4-3-Standalone-Builds-Really-Poor-Performance). Until then, it would be best to stick to 4.2.
