Picked up the Olive 998s, but need help with sizing

Can anyone provide guidance on what size I should stick with? I measure close to 8.5 on the Brannock device, and I typically between 8.5 and 9 and prefer a looser or roomy fit. My 990v6s are size 8.5, and my 991v2s are a size 9. There's definitely less volume in the toebox than I thought, but I'm guessing it'll loosen up and stretch? I just don't know how much it'll stretch and all.

Any guidance would be appreciated!