But, is that wired memory (actually in use by apps/libs) or cache memory (file cache, buffer cache, VM cache, etc)?
Remember, "free" memory on FreeBSD is wasted (unused) memory. The kernel tries to use any "free" memory for cache. On a properly working FreeBSD system, the "free" memory should be near 0.
Also, remember that KDE re-uses a lot of shared libs/data, so the memory usage reported by top will not be an accurate reflection of the actual memory usage. Top doesn't show shared memory resources correctly.
There are several blog posts on planet KDE that cover this topic, and how most "memory checkers" get it wrong.