There's no IRS that will live long behind 900 horse. The 9" IRS that Heidt's and a couple other manufacturer's sell is probably the strongest... Built correctly the 8.8" will do ok, especially on the street where high horse usually just blows the tires off the car before it will hook hard enough to break many parts. If you do in fact build that much horsepower and have enough suspension and tire to hook it up, best stick with a solid axle 40 spline 9".