I would hold and shoot some double stacked .45 before you settle on one. They are much bigger than most people realize at first and many can not get a proper purchase on the grip to shoot them well. If it works for you, I think the G21 is a great gun. If the Glock is too big, I LOVE the Ruger P345. Poly frame, 8+1 capacity, Da/Sa like your P89, built like a brick, and very accurate (I belive this was the gun Mas Ayoob used to use both on Duty and in IDPA before switching ove to M&P). And it will be easily $50-100 less than the Glock of XD and less than half of what a decent 1911 will cost, and much more reliable.