1. With only 6 rounds, yes you will be at a disadvantage. You will be competing against others with 8 or 10.
2. Some clubs go strictly by the rules and while I can't find/remember the one rule that applys, let's just say magazine carriers are strongly encouraged at those clubs.
I agree with the other posts. "Run what you brung". What ever you feel comfortable with is what you should use.
At our club, Pitt County Wildlife Club in Eastern NC, we don't turn anyone away. SOMEONE there always has an extra mag holder, extra holster, heck, even extra guns have been loaned on occasion, for new shooters to use. We believe the more people we can get into the shooting sports, the better off we'll all be. We even had a guy shooting his SAA.....in IDPA!
He didn't win.....but he had a blast and was back next month with a 1911.
One more tip and I'll hush, You can't miss fast enough to win!
Take your time and make your hits first. Don't try to run with the big dogs......it won't work, trust me, this is the voice of experience.....BTDT! You have to remember, you're not competing with them. Your speed will improve as you practice.
Blessed are they who, in the face of death, think only about the front sight.