I have never thought too high about programming in C, however I often find myself blaming Mediocre for being slow due to being programmed in Java.
Anyone programming in C will tell you that it is lightyears faster than Java. And anyone programming in Java will tell you that the difference is negligible.
I tend to end up somewhere in the middle. Not being a superstar programmer I think that whatever speed advantage I might potentially get with C will be lost in sloppy coding.
However, just to see if there really is a difference I have started sketching on a C chess engine I call Sagan.
I am mainly doing this to not have any excuses for the engine playing badly. :) I hate the "well it's not strong, but you can only expect that from Java".
This is just in the planning stages for now. Studying at 150% speed does not give much room for anything but planning. :)