We have made significant improvements over the last year or so. Some random examples:

https://about.gitlab.com/2016/02/25/making-gitlab-faster/

https://about.gitlab.com/2016/08/22/gitlab-8-11-released/#pe...

https://about.gitlab.com/2016/07/22/gitlab-8-10-released/#pe...

An exact list of all merge requests related to performance (at least the ones tagged with "Performance") can be found here:

CE: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests?scope...

EE: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests?scope...