It pretty much comes down to the quality of barrel... You could put a Krieger barrel on a DPMS upper/lower combo and it would shoot head to head with the GAP and Fulton.
The mass acceptance of the AR platform in general has really pushed the minimum expected quality bar up pretty high!
Now you're trying to be realistic about this. The thread is supposed to be a GAP lovefest based upon one shooter and one rifle being extrapolated to a universal conclusion - "GAP10 Most Accurate AR-10 type rifle."
The fact is there are probably 3-4 manufacturers that can match the accuracy - with the shooter having the greatest effect. For example, I have no idea how Les Baer shoots his test targets - but, I can tell you the two 5-shot groups provided with the rifle look like slightly enlarged, ragged .30 caliber holes. Meaning, Les is one hell of shot (yes, he shot the test target - it's signed by him) and I wouldn't doubt he could do the same thing nearly any day.
The best I've been able to do with the rifle is one hole that's about .50 caliber in size for 5 shots - slightly smaller than a nickle where Les' targets are less than a dime in size.
For my use, none of that matters - I'm using it for precision tactical rifle and the second time I took it out after getting the scope sighted - I hit a torso steel target at 900 yards with repeated shots - in a variable cross wind. Took 3 shots to get the elevation dialed into the scope, and one shot for the crosswind - and then you could just pull the trigger and repeat the hit on the target.
I shot 5 shots, and then turned the rifle over to a friend, told him where to put the cross hair for windage, and he repeated the multiple shots. Neither of us are talented, practiced long range shooters - but, as I'm fond of saying - "I'll take luck over talent any day."