For your purposes, pretty much any distro will do as they all use the same kernel, which is the bit that's likely to impact on your response times. I doubt very much whether you will experience problems with regards to timing as Linux and Windows are two very different systems. In Windows for example, one of the major causes of latency is the user interface, which is essentially a part of the operating system. Under Linux, the user interface is an entirely different process and can be turned off if it's causing you performance problems. (or you can use alternative / potentially better performing user interfaces .. or indeed you could write your own!)
If you do find you have issues, there are two kernels you could try, the standard kernel (which itself has a choice of 'schedulers') and the real-time kernel, which is going to be about as close to 'wire speed' as you're going to get from a PC. On ubuntu for example, all that's required to grab the real-time scheduler (on Ubuntu) is;
apt-get install linux-rt
But again, you shouldn't need this. For some technical background, try;
http://www.ibm.com/developerworks/linux/library/l-scheduler/
