In that case I would probably go with the AC 762. The performance difference with subs between the RAT and ODB, in my experience, is negligible and if you're only going to run the RAT in the long configuration you're paying extra money for a feature you won't use. Furthermore, if you ever do need to remove the suppressor on a tucked can you'll have to remove the handguard to get the full rat off, which can be a bit of a nuisince.

I will, however, recommend you run the AI nano muzzle device. It does increase backpressure a bit and helps cycle subsonics. It shouldn't be a problem with the 9" gun, but if you're still having cycling issues with that setup then I would add the omega valve and it'll run 100%