Why the need for speed mate ? Unless you're doing HFT, which you're not or you wouldn't be asking, MT on Windows is fast enough for most trading.
Using JAVA and/or API's will narrow down your choice of brokers a lot.
Oanda did a REST API recently which is language agnostic, can use anything you're currently using, long as you can generate htpp links via the code.
I'm on Oanda's JAVA API, they also have FIX and C++ versions, it's probabaly the best in the market at the moment. I'll be migrating to REST API using JAVA eventually I guess, soon as their functionality gets better.
If speed is that big an issue you night want to look in that direction.