Arrow flight is everything, if your only getting marginal flight from your arrows, I'd get some new ones if possible.
If everything looks good out to 15yds, then your golden. My only worry about having such a heavy shaft and low bow weight would be deer ducking the arrow. Kinetic energy can suffer if your arrow weighs too much, which is critical with such a light set-up.
If you went with the recommended 10-12 grains per pound, your arrows would weigh between 390-468 grains.
Maybe others have had good luck with the set-up your describing. In my honest opinion, I would try and find a weaker spined shaft and shave off 100 grains.
Maybe someone will be willing to trade you some shafts for the ones you have, or buy 3-4 different sizes to play with.