[string[]]$nums = Get-Random -Minimum 1 -Maximum 100 -Count 100kb

measure-command { $nums -join ','            } |% TotalMilliseconds
measure-command { [string]::join(',', $nums) } |% TotalMilliseconds

234.82690000000002
14.497100000000001

$w1 = Get-Content d:\test\wordlist.txt;   $w1.Count
$w2 = ${D:\test\wordlist.txt};            $w2.Count

measure-command { $w1 -join "`r`n" } |% TotalMilliseconds
measure-command { $w2 -join "`r`n" } |% TotalMilliseconds

measure-command { [string]::join("`r`n", $w1) } |% TotalMilliseconds
measure-command { [string]::join("`r`n", $w2) } |% TotalMilliseconds

172823
172823        # same word count

254.6534
423.63100000000003    # <-- slower?

183.01510000000002
16.148400000000002    # <-- how come this one is SO fast?