５４２の方法
procedure TForm1.Button3Click(Sender: TObject);
var
  sl1,sl2:TStringList;
  i:integer;
  start,stop:DWORD;
begin
  sl1 := TStringList.Create;
  sl1.LoadFromFile('c:\Test1.txt');

  Start := GetTickCount;

  sl2 := TStringList.Create;
  sl2.Sorted := true;
  sl2.Duplicates := dupIgnore;
  for i := 0 to sl1.Count-1 do sl2.Add(sl1[i]);

  stop := GetTickCount;

  Label3.Caption := IntToStr(stop-start);
  Label4.Caption := IntToStr(sl2.Count);
  Memo1.Lines.Assign(sl2);
  sl1.Free;
  sl2.Free;
end;