You know, I'm just starting to try out something where I try to solve it before a song end. I start both at about the same time(the song always starts first). I'm a big Pearl Jam fan, so I have a lot of songs of various lengths that could work. Right now, at my current (slow) clip, PJ's cover of "Leaving Here" is about right to give me a challenge(~2:45), but I really want to eventually be able to beat "Lukin"(1:02) consistently.
Edit:"Green Disease"(~2:40) is probably better than "Leaving Here".