I think Dana 60's are rated as the most efficient rear end due pinion location in relationship to the ring gear. There are some articles directly comparing the GM 12 bolt to 9" outlining a 2-3% efficiency gain in favor of the 12 bolt. Lower pinion location strengthens the contact pattern, but in turn sacrifices efficiency which is typical of the drop out carrier models. I like the Dana 60 route, built one for my wife's Duster because it was cheaper than finding an 8 3/4. I like the pinion shim setup in the Danas better than GM's 12 bolt design even with a solid sleeve in place of the crush sleeve.