Seems pretty good for the most part.
I only noticed one glitch when the server reached 3,200 which concerned me a bit, however, it did not appear to be a phpBB3 issue from what I could tell... more of a load problem.
Though a RAID should have no trouble handling at least 20,000 users online at the same time, so I don’t know why it had that glitch.
EDIT: Ah, gotta LOVE POST REVIEW!! haha!
Actually, I’m surprised at the Hardware, I would think phpBB would need/choose something with a bit more power.