Do Underdrive pullies hurt...

It seems like this is a question that is asked alot. I myself have not yet done this to my 06 GT. I have read that the gains on the 05 + are not that significant. I also am concerned about an all alloy engine block. My 2000 and 2003 GT's had good gains with out any notice in temperature rise or alt problems. The only time I noticed my temp rise was at the track. I believe this would have happened anyway. By the way I live in Texas and being hot here is an understatement. Hope this helps.