Some question regarding script performance?

I have some question regarding autoit performance?

lets say i have a 2000 line of text, with max 30 char / line, I would do something big for each line, what should i do for best performance?

Dim $aList
_FileReadToArray($MyFile, $aList)

For $i = 1 To $aList[0]
  Local $line = $aList[$i]
  ;I do something
Next

or

$hFile = FileOpen($MyFile)
While 1
  Local $line = FileReadLine($hFile)
  If @error = -1 Then ExitLoop
  ;I do something
WEnd

the problem is, I am going to copy this script and run it together, maybe 20 or 30 instance, each script will take about a couple of hours to complete, so what are your thoughts?