Just to a ping to the IP address, if they allow, to their server and that will give you latency. http://speedtest.net/ works very well for alot of general tests. Move the cursor to Chicago and run test and see what your latency is. To the OP from Europe to US around 200 ms of latency is normal and fine unless you are trying to HFT obviously. There is also a program called ping plotter that will actually show the detailed info.
Time at exchange ack, minus time sent. For IB this is (time when orderStatus = SUBMITTED) - (time at placeOrder). From Australia, I see 300ms to 900ms against the IB test market for ES. Pretty hard to arb anything at those latencies..