Inserting string into the beginning

I've used code submitted earlier on this forum:

#Include <EditConstants.au3>
#Include <WinAPI.au3>
#Include <WindowsConstants.au3>
Global $sFile, $hFile, $iSize, $sData, $tData, $iRead
$sFile = @WindowsDir & '\regedit.exe'
$iSize = FileGetSize($sFile)
$tData = DllStructCreate('byte[' & $iSize & ']')
$hFile = _WinAPI_CreateFile($sFile, 2, 2, 2)
_WinAPI_ReadFile($hFile, DllStructGetPtr($tData), $iSize, $iRead)
_WinAPI_CloseHandle($hFile)
MsgBox(0, '', Hex(DllStructGetData($tData, 1, 1), 2) & Hex(DllStructGetData($tData, 1, 2), 2) & ' (' & Chr(DllStructGetData($tData, 1, 1)) & Chr(DllStructGetData($tData, 1, 2)) & ') - signature for EXE fies.')
$sData = ''
For $i = 1 To $iSize
$sData &= Hex(DllStructGetData($tData, 1, $i), 2)
If Mod($i, 16) = 0 Then
	 $sData &= @CRLF
Else
	 $sData &= ' '
EndIf
Next
$sData = StringTrimRight($sData, 2)
Global $Edit
GUICreate('MyGUI', 422, 526)
$Edit = GUICtrlCreateEdit('', 10, 10, 402, 506, BitOR($ES_READONLY, $WS_VSCROLL, $WS_HSCROLL))
GUICtrlSetFont(-1, 8.5, 400, 0, 'Courier')
GUICtrlSetData($Edit, $sData)
GUISetState()
Do
Until GUIGetMsg() = -3

and it's working great! But I need to get the data in reversed order therefore I used

$sData = Hex(DllStructGetData($tData, 1, $i), 2) & $sData

It is working, but obviously it's painfully slow.
Does anyone have any ideas how to make the process quicker. I'd really gratefull.