My 2005 #0507 is a speedi sleeved car. For whatever reason, as everything seems to happen to me, most recently the power steering hose, speedi-sleeve'd car had a rear main seal leak at around 20,000 miles. My concerns of failure are about zero, it should hold up as well every other car, with or without.
One small note, before we tore the car down to do the work, we contacted Ford to question if mine was a speedi-sleeve'd car, Ford said no. I don't believe there is a known cutoff, and I don't think it makes any more or less than having the nice looking A - arms.
Pete S.