I don't have any numbers but I can tell you where we have noticed performance issues.
Our builds typically use 30-40K files from source control. In my workspace currently there are over 66K files including build intermediate and output files, over 15GB in size. To keep AccuRev working responsively we aggressively use the ignore elements so AccuRev ignores any intermediate files such as *.obj. In addition we use the time stamp optimization. In general running an update is quick, but the project sizes are typically 5-10 people so normally only a couple of dozen files come down if you update daily. Even if someone made changes that touched lots of files speed is not an issue. On the other hand a full populate of all 30K+ files is slow. I don't have a time since I seldom do this and on the rare occasion I do, I run the populate when I'm going to lunch or a meeting. I expect it could be as much as 10 minutes. In general source files come down very quickly, but we have some large binary files, 10-20MB, that take a couple of seconds each.
If the exclude rules and ignore elements are not correctly configured, AccuRev can take a couple of minutes to run an update for workspaces of this size. When I hear of other developers complaining about the speed I know something is miss-configured and we get it straightened out.
A year or so ago one of the project updated boost with 25K+ files and also added FireFox to the repository (forget the size but made boost look small.) They also added ICU, wrote a lot of software and modified countless files. In all I recall there were approx 250K+ files sitting in a stream. I unfortunately decided that all their good code should be promoted to the root so all projects could share. This turned out to be a little beyond what AccuRev could handle well. It was a multi hour process getting all the changes promoted. As I recall once FireFox was promoted the rest went smoothly - perhaps a single transaction with over 100K files was the issue?
I recently updated boost and so had to keep and promote 25K+ files. It took a minute or two but not unreasonable considering the number of files and the size of the binaries.
As for the number of streams, we have over 800 streams and workspaces. Performance here is not an issue. In general I find the large number of streams hard to navigate so I run a filtered view of just my workspaces and the just streams I'm interested in. However when I need to look at the unfiltered list to find something performance is fine.
As a final note, AccuRev support is terrific - we call them the voice in the sky. Every now and again we shoot ourselves in the foot using AccuRev and wind up clueless on how to fix things. Almost always we did something dumb and then tried something dumber to fix it. Eventually we place a support request and next thing we know they are walking us through the steps to righteousness either on the phone or a goto meeting. I've even contacted them for trivial things that I just don't have time to figure out as I'm having a hectic day and they kindly walk me through it rather than telling me to RTFM.