Faster Screen Clearing?

Even with random drawing and page flipping, it still seems faster to use DrawRect() instead of Cls(). ?

SuperStrict
Global start_time:Int
Global end_time:Int
Global l:Int
'
HideMouse()
'
SetGraphicsDriver D3D7Max2DDriver()
'SetGraphicsDriver GLMax2DDriver()
Graphics(800,600,32)
'
'
' Test 1: using DrawRect() to clear the screen
'
'
start_time=MilliSecs()
For l=1 To 2000
 SetColor(0,0,0)
 SetAlpha(1)
 SetScale(1,1)
 SetRotation(0)
 SetBlend(SOLIDBLEND)
 DrawRect(0,0,800,600)
 drawbox()
 Flip(0)
Next
end_time=MilliSecs()
Print end_time-start_time
'
'
' Test 2: using Cls() to clear the screen
'
'
start_time=MilliSecs()
SetClsColor(0,0,0)
For l=1 To 2000
 Cls()
 drawbox()
 Flip(0)
Next
end_time=MilliSecs()
Print end_time-start_time
'
ShowMouse()
'
Function drawbox()
 SetColor(Rand(255),Rand(255),Rand(255))
 SetAlpha(1)
 SetScale(1,1)
 SetRotation(0)
 SetBlend(SOLIDBLEND)
 DrawRect Rand(600),Rand(400),200,200
End Function