I have done 5 track days on Booger, (my black, 06 Thruxton) and one on Tweety, the yellow 06 Thruxton that I bought specifically for trackdays. My purpose for doing trackdays was just to improve my skills. I am pleased to find that, while I remain embarrassingly slow, my skills have definitely improved. When cooler weather returns I will resume my much needed education.
To answer the question, the Thruxton is never going to be as fast as a sport bike. However, 90% of what happens on the track is due to the rider. You will find that you won't be riding this bike like a sport bike, your style will be a little different. However, since I started with the Thruxton, I don't know the difference. I just see it in the pictures of myself and other riders. The bike remains better than I am.