Let's show forum stats as a timeline graph (with supporting table below it). Show for the whole tool the # of posts per day. At longer time intervals, aggregate to a month. We've done some testing with mongodb aggregation queries [#6081] and with some index, it should be fast enough we think.
Page layout similar to SourceForge download stats, e.g. https://sourceforge.net/projects/openofficeorg.mirror/files/stats/timeline is what I'm thinking