I've had good luck with self-hosted GitLab's performance in my small group, but I've heard tales of others who haven't, so try before you buy if you're doing that. The CI integration is really nice though and GitLab has put good work into that flow. It can also be the cheapest option and keeps you self-reliant if that's something that appeals to you.
Indeed, most people don't need to host repositories that large but we're proud that our performance scales out even to repositories that are massive.
(ObDisclaimer: I work on VSTS.)
For self-hosted GitLab instances run on a smaller scale, there should not even be a chance of performance hits :).
Just to give a good overview of what GitLab is offering for both self-hosted as well as our hosted solution of GitLab.com please look at https://about.gitlab.com/features/
I am happy to hear that the CI/CD integration, which is our native solution for CI/CD and beyond is being well received! We want to persuade not force users to use our native solutions.
It will take a lot to prove to us that hosted Gitlab is actually good performance "for reals this time".
We're also working on an entirely new storage architecture for scaling and are slowly rolling this out. You can see more here: https://gitlab.com/gitlab-org/gitaly