We used to run Gitlab Premium for around 300 users running hundreds of jobs over some monorepos. Gitlab suggested a small architecture using Omnibus, and while it helped a bit, it didn't perform as well under load as we expected it to.

Eventually, there was no virtual scaling that could help. This, for me, is the biggest problem with Gitlab hosting: as soon as you hit a scale where a single machine with Omnibus doesn't cut it, the jump in complexity, cost, and engineering hours is significant.