You should have the daggerboard pulled up quite a ways on a r each so it makes no difference how long the board is. Where did you get a 29 inch board? That seems pretty darn short for a Sunfish. Is it some homemade thing?
The daggerboard has little influence on up wind stability. In high winds it can help to pull the board up a few inches so you do not have to hike so hard. But with your 29 inch board you'd mostly be side slipping anyway.
1. You'll go faster forward with a longer daggerboard vs sideways we could barely tack with the small daggerboard that came with our early wooden Sunfish. It was great on a run...
2. What BB said, and longer daggerboard helps with tacking.