I agree with smrobs about the twisted wire bits. Be careful. I use one on my top barrel horse but I only have to have a very light hand with her. I would suggest stepping back a notch and working on your basics again (walk/trot until you see god, then canter) Like smrobs said, there is no magic bit...also im not a fan of tom thumbs for speed horses (just my opinion and experience talking) but I have had alot of success with the o-ring snaffles, sliding gag bits, the wonder bit, and the "quick stop".
Full time trainer of 1D barrel horses.