Was running a 13/21 cut back 5mm in a 14 vein skat mag with 50 full specs, rrp pipe, msd total loss, 210 psi, etc in my carbon badass and still have the prop on the shelf as well.
11-12 will be very close for you on the bottom, the 5 port pulls hard up top I’d be in the 19-20 range personally...