I use the lightened steel on the front, and plastic on the rear running 19T.
I have only damaged one rear outdrive and the only reason was I side swiped the wall fairly hard (ruined hub bearing, broken hub carrier) which caused the dogbone to pop out and chew up the outside of the outdrive.
I would have bought the IRS outdrives, but for the price and my ability I felt they were unneccessary.
Oh yeah, do NOT use them with the stock pincushions, they will wear the IRS drives out in no time. If you use the IRS outdrives, get the IRS pincushions.