Sorry to be negative but GitLab's performance is embarassing :/ It is so slow and it's not clear why. Is this because of rails? Just seems very poorly engineered.
I don't know where people get the notion that rails is slow.
I have shipped large rails apps as packaged software for on-site install (using jruby). It's not easy.
If your local database is slow and the app code requires lots of DB resources, then sure...but that's the app, not rails.
Github on the other hand can use strategies solely targeted at their SaaS performance. It seems that Github also maintains more control over their enterprise version than Gitlab but I'm not 100% sure there.
https://github.com/github takes ~2.2 seconds, but by about 1 second has most of the information on screen and is simply waiting for the activity graphs.
We're working really hard on identifying the causes of our performance issues, as well as fixing them.
There's a META issue about this here: https://gitlab.com/gitlab-com/infrastructure/issues/947