Unless you do some really fancy footwork, you're not likely to get good accuracy much past 28.5 grains of powder.
I'm glad you started lower than what I recommended. I had thought that the weights I mentioned would put you right in the 1800fps-1900fps range, but obviously I missed my guess pretty badly. I believe your rifle has a 1-10 or 1-10.5 twist rate, and that will make it very difficult to achieve accuracy at speeds greater than 2000FPS.
I believe the accuracy you saw in the 27.5-28 grain range will indeed prove to be your accuracy load.