FWIW the 8.75 (OE housing) has held up well for me with street + HSAX use, 590'ish HP and a manual transmission. I run the clutch type sure grip and Moser axles. Also 200 treadwear tires.

With tapered bearings, it takes side loads well.

If I did upgrade, I would be looking for a stronger axle that could handle sticky tires (eg 50 treadwear) along with the HSAX standing start and manual transmission. Likely a Dana 60 though an aftermarket 9" could do it also.

Comparing to an 8.8 I agree save your money. Use the 8.75, add sure grip of your choice and Timken bearings. Stronger axles would not hurt but not really essential IMO.

Also lose the drum brakes... from first hand experience, they do not like hard track use. The Dr Diff rear disc kit has worked well on my 8.75.