I have taken both my ARs to the range the last couple of trips. One a 16" midlength and the other a 14.5" Carbine with pinned FH (toget legal 16" length).
I run the same ammo through both of them and sight in with the same combo of rounds as well. I use Black Hills to sight in and then plink with cheap Monarch. I run equal amounts through both.
Each run 9mm RRA buffers.
The midlength has less kick and has never short stroked even with the cheap Monarch. It's also the cleaner of the two when it comes time to clean.
I'm a Middy fan. The only negative on the Middy I have is that it's HBAR and a bit heavy, but for me the weight is not an issue.
Not sure why the OP wants a 1/9 twist. The RRA I have has the 1/9. Bravo Company sometimes sells 1/7 twist uppers and CMMG does as well. You will pay more for the CMMG, but then again they have the Med-Con option as well as the HBAR. Pretty sure the RRA was the cheapest of the bunch. 1/7 is the better option in eth fat you can run a 77grn bullet, but realistically I am happy with my 1/9 and 55-66grn bullet choices.
Most middys are 16". I like this option as it allowed me to change the flash hide to something more evil. Only reasonably priced shorter middy would be the CMMG in 14.7".
Here's my 16" with "evil" FH and bolt on FSB.
If you just want the added sights, you can run a CAR15 and a bolt on Sight base and under gaurd gas block to get a more "Dissapator" look/feel.