Sticking with 3-shot groups for a break-barrel is the best choice I think, it's what I use for my Encore and Optima Elite as well as my BLR. My load work is done from start loads, 3 rounds each increasing in ½gr increments, allowing the barrel to cool between each 3 shot group. I've had many, many range trips where that ½gr difference made all the difference in the world, it could go from a 3" group to a ½" group with just the ½gr change, so if you're loading in 1gr increments, you could easliy miss the sweet spot.
I wouldn't hesitate to load warmer than 56gr, their max in the #4 manual is 57.5gr @3.330" COL for the 200gr TSX, if you're loading longer, you can easily increase above their max, in ½gr increments, a sticky barrel release will likely be your first sign that you're approaching a little too much pressure, on an ejector barrel it's usually sticking brass, flattening of primers being the usual suspect too.
Tim