If you run it on your own server, it's quite usably fast - gitlab.com is super slow.
I don't have any experience on the matter though. my previous job used bare SSH-Repos and my current one uses Stash/Bitbucket.
(Though can't tell about the last two versions - we skip versions if not impressed and/or when we wait until something is finished (like e.g. the new ui now). We never update to x.x.0 as there is always an improved x.x.3 or so version worth waiting to).
For a really small team with 6 developers and maybe 3 CI builds per hour, I had to give the Docker container 7GB ram to run well. (not including the CI runner)
It's ridiculous that it would need that much for a small setup, but any less and page load times get very slow.