If you're American, the best option for you (and your 6 digit account) is an American Company too (think Buffet - ize your own).

And in case it bellies upward (such as Refco, FXQL, 1World, UGM etc), you have the all mightly NFA, CFTC to blame for their very great policies.

This so called safe broker for large deposits is just another one of those the Holy Gay threads.

Personally, I'd rather commerce on multiple brokers.