For a given amount of memory, interleaving may offer slight performance enhancement over single stick, as has been highlighted.
However, in almost every real-world situation, an increase in the amount of RAM (4-fold in this case) will improve overall system performance by reducing the amount of paging from RAM to disk.
Not all OSs can make use of large amounts of RAM - particularly 16-bit OSs like Windows 9x, so there isn't much point in throwing RAM at them. Better to upgrade to a proper OS like Linux (but let's not go there!)
SD