OK, Here are my results. All of my tests lasted 60 seconds.

EXECUTE
Execute kept climbing the whole time.
Start: 172,532 K
Finish: 191,420 K
Difference: 18,888 K

code:
Break on
$x=0
do
	$=execute("$$x=kbhit()")
until $x
CALL
Call kept climbing the whole time.
Start: 172,368 K
Finish: 179,836 K
Difference: 7,468 K

code:
Break On
$x=0
do
	call ".\test-code.kix"
until $x
TEST-CODE.KIX
code:
$x=kbhit()
RUN
Run held steady.
Start: 172,532 K
Finish: 178,552 K
Difference: 6,020 K

code:
Break on
$x=0
do
	Run('%Comspec% /C Dir .\ > Nul')
until $x
SHELL
Shell held steady.
Start: 172,564 K
Finish: 173,340 K
Difference: 766 K

code:
Break on
$x=0
do
	Shell('%Comspec% /C Dir .\ > Nul')
until $x
WMI
WMI held steady.
Start: 185,336 K
Finish: 186,636 K
Difference: 1,300 K

code:
Break on
$x=0
do
	$Locator = CreateObject ('WbemScripting.SWbemLocator')
	$WMIConnect = $Locator.ConnectServer('.', 'root\CIMV2', $AdminName, '"' + $AdminPassword + '"')
	$WMIConnectError = @error
	IF $WMIConnectError = 0
		$WMIConnect.Security_.ImpersonationLevel = 3
	ENDIF
	$Locator = ''
	$WMIConnect = ''
	$WMIConnectError = ''
until $x
Hope this helps.
_________________________
Kelly