mojoPortal was built to be efficient and scalable but I don't have any sites getting enormous traffic that I can point to, maybe someone out there is using mojoPortal for a large traffic site and can post some more info about their performance.
I know there are some DotNetNuke sites that get a lot of traffic and I have done some load test performance comparisons between DotNetNuke and mojoPortal
here, and mojoPortal performed significantly better on the same hardware than DNN.
This site gets moderate traffic but not nearly enough to push the hardware to the limits, but I believe mojoPortal makes efficient use of resources and will support very large traffic sites.
Hope it helps,
Joe