How much wind do you have when the wather helm starts? What effect does reefing have when weather helm starts?
I have a Pearson 28 and put in a reef at about 15kts to relieve wheather helm, and increase boat speed. Before I bought new sails, I couldn't reduce weather helm to an acceptable degree regardless of adjustments made. I also went with a loose footed main on the new sails and I'll bet that also helps reduce weather helm.
Reefing is cheap.