Generally speaking, 'good' accuracy is .5" at 100 yards (measured center-to-center). With your 1.25" group, I would consider doing something a little more drastic than adjusting your powder charge. I would consider a different bullet or a different powder (a buddy of mine that shoots a 270 gets good results with H4831 and I get similar good results with the same powder in My 280 - Updated!
Also, when making powder adjustments, .1 is probably too small. With a 50+ grain load, 1% is .5grains. As a result, your strategy of going in .5grain increments is a good one, then if you want to fine tune I would look at .3 and maybe .2