you'll hit the rld cap very early no matter how you class the 3rd time.
if you class ACC, you'll hit accuracy cap 1 or 2 levels sooner than if you class them Rld.
Your gunners will reach the accuracy cap no matter what, assuming you have them BVE-ed.
to give you an example, my 9/12 rld-rld-rld gunners reached the accuracy cap at around lvl 100.
If these are your first pair of gunners, then you should class ACC, just so you can reach both caps sooner.