Need help! 3.625" or 4.625" Backspacing?

[91GMCSuburban]

which should I go with? 3.625" or 4.625" Backspacing.

15x10 wheel w/either
1) 35" on 4" lift + 2.5" reverse shackle, extended front shackles. So I guess about 6" total.
2) 33" on 4" lift

 

[91GMCSuburban]

C'mon guys, I need help.

 

[91GMCSuburban]

ttt

 

[Triaged]

3.625 on 8" wide rims

or get 17" wheels in 9" wide.

Edit:
FWIW the 17" wheel comment was so you wouldn't run into the problem I did with having to grind the hell out of your calipers when you go to 8-lug after breaking the 1/2-ton axles. It will save you $$$ in the long run only having to buy new rims and not rims and tires.