1) I gifted x oz of gold to our sons, which they would then sell
Keep in mind that the gift beneficiary keeps the gift giver’s basis. So your sons will also be taxed at the collectibles rate on the same gains that you would have. If they were to inherit the gold instead, they would get a step up to a new cost basis (if the gains still remain). If you are also giving inherited stocks, rather than money, to your sons, you need to let them know what the cost basis of the stocks is, so they can be correctly taxed when they sell.
3) each of these would be non-taxable events but net the same to both parties, and
Nope - the sale of the gold that you posited in your first statement would be taxable to your sons, so they would end up with less than you intended to give them.
AJ