Finding all files greater than 1GB with Powershell:
Get-ChildItem -recurse -force -erroraction silentlycontinue | where {$_.Length -gt 1Gb} | ft
If you want to find the 5 largest files, use the following:
Get-ChildItem -recurse -force -erroraction silentlycontinue | where {$_.Length -gt 1Gb} | sort-object -Property Length | select-object -Last 5
This is a bit clunky and slow, but can get the job done. See sample output below: