...Why would I prefer to possibli open a 1 contract position with IB instead of a 10 contract position with Ninjatrader with my 5000 account.
Why would you prefer one over the other? Here, try this...
On the same day...
In sim account A, open a 1 contract position and watch it.
In sim account B, open a 10 contract position and watch it.
When comparing the two...
You'll prefer B when the trade works.
You'll prefer A when it doesn't.
And if you go by the standard statistics everyone touts about failure rates, you will prefer A in both cases because B can go too wrong, too fast.
If you want the specifics about what IB really requires you should call them and ask, because I am sure somewhere on their website it says that requirements are subject to change at any time and the website may not be current.
