I prefer the 9" just for the gear changes... Never have broke one. The one in Rog's Comet has probably 500-600 passes on it with only 1 bent pinion, and the gear company replaced that gear set for free. 12 bolts are also a bit more difficult to set up IMO. Parasitic horsepower loss is minimal, maybe 5 or 6 horsepower. If there good enough for 90% of the door slammers at the drags, should say something about which is preferred and their durability.