I haven't used GateIn, but we've used Liferay For a couple of production sites and have been pretty happy with it.
Enterprise features that we've used extensively:
- multi-site (for serving web and mobile versions)
- structured content (for templating shops, restaurants, etc)
Performance has been troublesome for us in the past. There is/was a bug in the version of Liferay 6 we were using that caused database connections to be exhausted which would bring down the admin site and required a reboot. But once patched db performance was good. I believe ythis bug is resolved in the latest version anyway.
Tuning of Apache and Tomcat also took some work. OOTB Apache was spawning a lot of processes which chewed up memory. Again, once the tuning was complete we had no further issues and are now seeing 100% uptime.
Hope this helps. If you need any specifics on the bugs, I can probably dig them out.