Any experience with wheel adapters? Need help with sizing...

Asking for advice from those that have used wheel adapters

I know there's a lot of negative thoughts surrounding the use of wheel adapters, but I'm going to do it... My car is not a daily driver and I want something different than what the SBP options are...

I'm currently running SBP 15x7 Cragars w/ 4.125 backspacing, if I add wheel adapters that are 1" thick, then I would need to run 5.125 backspacing on another 15x7 wheel to achieve the same clearance between the tire and the fender, right?

what would be the equivalent backspacing on a 15x8 wheel? around 5.5?