I was in the same boat for a few years, shooting motorsports with a P/S. The 2 seconds per frame, the half a second of shutter lag. It was painful. The pictures were great but I just needed more.
I had some old (really old) Canon lenses laying around from my wife's hay-day in film photography, so I decided to go with Canon. I bought the best I could afford at the time: a 50D. It was cool because it had a "sports mode" on it. Didn't take long for me to realize that I didn't know squat about real photography. Yeah, I could take good pictures, but when I tried to match my skill with the Sony P/S using the 50D I was seriously depressed.
I stuck with it, traded my 50D for a 7D (it has video), and am trying to learn how to take real pictures all over again without the benefit (hindrance) of a sports mode. It's not easy. Especially when I could churn out good stuff with the old Sony. But I'm sticking with it and getting much better with my old glass. Got a long ways to go, and love learning, so it should be a fun experience.
Just remember that buying a good camera doesn't make you a good photographer, and that you're probably going to have to learn all over again. But it's worth it.
Just buy what you can afford (Nikon or Canon or...?) and dedicate yourself to learning. You'll be happier for it in the long run.