if you need latency data, and that being for data as well as round trip for internal processing time as well as round trip of your order from server through brokerage, off to trading venue/ECN/exchange and back, your broker or most savvy brokers would be HAPPY to provide that. If not, or the old "well, I'm not sure, but it's LIGHTNING FAST!" It's probably not a broker you would actually need. You can get this data quite easily by contacting the brokers. If they're good, they'll have it or be happy to provide/test for you.
Apologies for the late reply. It depends on what type of trading you will be engaged in, whether you are planning on getting an exchange seat (lease or purchase), etc. If you are not planning on getting an exchange seat, then the direct connect to exchange (i.e., Globex) will not be available to you. In which case, you will have to stay with IB, or some other broker that specializes in automated trading (i.e., Lime Brokerage or RedSky, both have favorable comments). These brokerage may not necessiarly offer a FIX based order routing, it maybe API based.