Here's my 2 cents.
If you are really 100+ plus a day and are prepared to work on 25 times (4% margin)leverage as you say, you can connect with prime brokerage.
There are couple of tiers for high volume traders.
Look up
http://www.hsbcnet.com/hsbc/online/e-fx-solutions
you will see that you can access Currenex, FxAll, Reuters FX, etc.
Make sure that the broker is not a counter party to your trade. This is important because you do not want a situation where for you to make money your broker has to lose money. You want the broker to be a neutral party, making money only from your trades as commission.
Other info on instituitional platforms such as Currenex, FXAll can be obtained by typing Currenex prime brokerage or white label and you see the platforms available.
Hope it helps
Cheers