I just switched from a 32-bit distribution (Ubuntu Karmic) to a 64-bit distribution (Ubuntu Lucid). On my 32-bit system, Iron was just as stable as Chromium. However, on my 64-bit installation, I often get "oops" and I need to reload the page. Of course, this could be due to a buggy flash implementation, but Chromium 4.0.306 seems to be a lot more stable (like on my 32-bit distribution).
Is it possible the build process of Iron has some problems with 64-bit? Or are the latest commits (from 4.0.275 to 4.0.306) bug fixes for 64-bit? Well, I hope the Iron devs can fix this. I don't know what information I can provide to help you prevent those "oops" pages, so please tell me what I can do.