I was surprised to find out that 28 spline 9" rears only weigh 10 lbs more than a 5 lug 8"... The housing is 2 lbs more, and the chunk is 8" more. You can get the lighter 9" stuff for good prices, so I don't see a difference other than the 9" is WAY stronger. If you go with large bearings, big axles, and all the frills, the difference is 16 lbs... but then you can handle several SBFs at once! This is using heavy duty parts... You can still get gun drilled and scalloped axles among other things. Dave