On my laptop, with a fairly random set of files, I found that

[http://IO.Directory]::EnumerateFiles

….is a lot quicker than

get-childitem

….given that all I wanted was the filename.

Here is the test I did:

11:24 [1.83] C:\powershell >measure-command {$x = [IO.Directory]::EnumerateFiles("c:\temp", "*", 'AllDirectories')} | select milliseconds

Milliseconds
------------
           4


14:26 [0.02] C:\powershell >measure-command {$x = [IO.Directory]::EnumerateFiles("c:\temp", "*", 'AllDirectories')} | select milliseconds

Milliseconds
------------
           2


14:26 [0.01] C:\powershell >measure-command {$x = [IO.Directory]::EnumerateFiles("c:\temp", "*", 'AllDirectories')} | select milliseconds

Milliseconds
------------
           2


14:26 [0.01] C:\powershell >measure-command {$x = get-childitem -recurse "c:\temp"} | select milliseconds

Milliseconds
------------
         137


14:26 [1.14] C:\powershell >measure-command {$x = get-childitem -recurse "c:\temp"} | select milliseconds

Milliseconds
------------
         731


14:26 [0.74] C:\powershell >measure-command {$x = get-childitem -recurse "c:\temp"} | select milliseconds

Milliseconds
------------
         628