As stated above, the games being untouched on a separate partition does little good if you can't run them after a reinstall....; the newly installed OS would no record of them being installed, or 'maps' to where they are installed.
Best to just leave a single partition, IMO....; if determined to proceed (backing up/restoring JUST Windows is easier when it is smaller, as you suggest), you can shrink the existing partition within admin tools/computer mngmt/storage/disk mngmt, then create a new partition from the now unallocated space..