"In order for shooters to be able to compete with their peers, IDPA competitors are divided into classifications within each division based upon their skill level. IDPA has a very quick and easy method of classifying shooters. Only currently affiliated clubs may award classifications and only current IDPA members may shoot the classifier or be awarded a classification by a club."
CDP uses 45acp, but you'd find most 1911s there. you'd be in a disadvantage to shoot against those.
SSP mostly uses 9mm and 10rd capacity, larger caliber is not giving you any edge, only more recoil to manage.
如果 just for fun 的话可以先考虑参加你们local club 的IDPA Practice, 相信每个 IDPA club 每周都有一次 practice 然后每个月举行一次local match, 打local match的话不需要 IDPA Membership, 也不需要 Classified