I don't know just where this conversation got going between the 9 and the quick change, but as I read it seems to be centered around weight???
Strange has a redesigned and lightened 9 in iron center housing that I think he said they took 7 lbs off---
I have ran q-change under fuel cars for the purpose of lowering height of funny car and only issue was occasionally breaking the rear change gears-
In our rear engined dragster, I used a franklin center, Halibrand 3 inch axle, only one brake disc but with 2 calipers and Nance magnesiam side plates--broke the thrust side plate, built a billet 7079 alum one(was a bit heavier then) problem with that set up was with only one brake disc the heat from the brake was enough to loosen the splined hub on that side---and after breaking a set of change gears in a final somewhere--changed to ford 9 inch-
We ran the 4.86 ring and pinion because the ring gear was thicker and stronger than the 4.11--never had a ring and pinion problem---