I have to agree with everyone in that the bit isn't the problem. I DO know what I am talking about, because my horse, who is a very successful shown and proven showjumper can get VERY fast on a course of jumps and I have been through countless bits with him. He would also lean and as he got faster and faster, he would start to be on the forehand. My trainer assured me that the bit wasn't the problem, but I needed to work that out for myself. This was a few years ago, now. I still own the same horse and he is now totally different. He still is fast in the show ring, but has a lot more impulsion and is manegeable. What changed? Hours and hours of flatwork, using half-halts, serpentines, all the usual school figures and now that I have transposed this schooling to jumping I have no problems and my horse listens to me all the time.