I am working an a 8" 300 black SBR for fun (its just a pistol now), but am thinking about a .223 wylde SBR upper to play with cheaper ammo and to toy in any short range 3 gun matches I can run down.  The local range also has an informal rifle+pistol competition day once a year with a max of 50 yards.

I can tell the main reason for an SBR is quick handling.  I would guess then my suppressor is definitely out as you would not want the weight.

Is hitting power factor an issue?  I would think anything above 11.5 should still get 55grain bullets to power factor.  Or do people just use 69 grain and above to be safe?

If going SBR I would guess the barrel does not have to be top tier.  I would think 2 MOA is enough.???

To me a 14.5 is definitely out.  10.5 is too short for me.  I would be 11.5" to 12.5".  Interesting thing about 12.5 is some offer a midlength gas system. That might be interesting with an adjustable gas block. and I could get a rifle length handguard on it.

Thoughts???  and how are other people doing SBRs for competition.  

Another thing I notice about my carbines is the shorter grip is annoying to me.  I have long arms and like rifle length handguards and longer.  Maybe I should just look into a pencil barreled 16" with a 15" handguard instead.  Would this not be nearly as light and nimble as an SBR and close to as accurate???

there really is no power factor in 3 gun.  If shooting plates, as long as the plates fall you're good to go.
We see sbr from time to time.  
I've ran with an sbr for a few carbine matches.  No issues other than the fact the sbr really isn't  a competition gun.
I get faster times and splits using a more specialized 18" rifle

I'm shooting a 12.5" AR now in 3 gun (it is Compass Lake barrel with the CLE223 chamber) with a 1-4x scope, I have a 18" Rifle gas that I haven't tried out in a match yet but I don't think it would help much.  I've shot 11.5" Lightweight with a Red dot and 16" Middy with a 1-4x before.  I don't think in most cases there is a big accuracy difference and the if the gas systems are dialed in should not be much of a recoil difference.  Match coming up this weekend and I think I am taking my 8.5" 300blik for the first time (suppressed).  Plan is to use sonic loads on the long shots, and on the short stages to load up a sonic round for the last shot on the short stages to set off the timer.

There is a short-range monthly 3gun match I attend locally that is scored IDPA-style that I run a suppressed 11.5", mainly just for fun.  It has an adjustable gas block, so it is pretty soft and fast.  Got a 12" handguard that covers about half the flashhider/mount, so part of the Saker is under the handguard.

I run a 11.5 SBR, ironically it's more accurate than my 18' barrel with 55's. Its perfect for local matches with no shots past 150yds.