You can also try WinDirStat to finds out what is eating up space. Common things could be a large Hibernation file, which can be easily and safely disabled to free up space. You could also try temporarily reducing the Page File just to run your benchmark... Don't disable it completely, but reducing it's size can free up space especially of you have a lot of RAM. Just remember to set it back to "System Managed" after running your benchmark.
You could also try CCleaner. Run the Cleaner tool to find Internet cache files that may be taking up space. Just be aware that by default it will clean out your saved passwords, so make sure you take a look at all the check boxes and un-tick the things you do not want to clean.