Depending upon a number of factors, you'll pick up 1-2 fps for every 5 grains of arrow weight.
Based on that, I would also think you'd gain about 10 fps.
Not sure what your problem is but I know it's not the arrow itself (I shoot Maxima 350's btw and shoot them out of a Trykon XL and a Mathews SB). It's just basic physics so something else must have changed or your chrono readings aren't apples to apples. Are point weights and fletching the same? Something doesn't add up.