Need Help Finding the perfect barrel length for ASR Hub and suppressor.

About to wrap up my 300blk build but needing help finding out what length of barrel I need.

I have a 8inch slr helix handguard on the way and not sure if I should get a 8.3inch barrel or a 8.5 inch. I also own a lahar 30 and plan on getting a ASR Flash hider and HUB system. Really wanting a flush look but obviously if it's functional with the HUB. I think 8.5 would work fine but idk if 8.3 is pushing it.