You are going to get the best velocity with a 16" barrel, 300 is just a better performer out of a shorter barrel vs 5.56. You are still going to lose some velocity going from a 16" to say a 10" barrel, the loss just isn't as great with a 300 vs a 5.56. So to answer your question, no disadvantage...
I've recently got into 300. I abandoned all my 5.56 because I like it so much. However, I reload and it is convenient to have my black guns using the same projectile (308 and 300).
Im being dumb as well. My main point is I'd rather keep my weapon in a condition that allows me the most freedom to use it, legally of course. I view SBRing as a restriction upon a person's use of his firearm ( can't transport it interstate without notification, can't sell/gift it without more...
I don't understand why, the advantages over SBR are numerous, but to each his own. In all honesty, a foam cover over the tube of an AR pistol is just fine. 556 does not have enough recoil to prevent "cheeking" the tube from being a viable method of accurately making rapid follow up shots.
"This translated into $27.5 million paid to ATF in 2014 through Special Occupation Taxes from over 3,700 NFA manufacturers and in transfer and making taxes. "
This is why we still have the NFA and why it won't be going anywhere.