Well at that focal length you'll be hard pushed to get 50% keepers with a motionless subject, so 4% with a fast moving target is pretty good!! 1/30th is really pushing it, but you've definitely got the desired effect and feeling of motion here.
It's rare that I try panning (only generally in motor sports) but I always try starting off with a relatively fast shutter speed and then gradually getting slower, rather than going for what I think would be my ideal shutter speed from the word go. At least then I have some keepers in the bank.
Great shot. You know I love panning. Its one of my favorites when it comes to photography, that was what my teacher in photography first told me that was amazing. Right now I still try to master it so whenever I have even a slight panning picture, I go crazy. ) so good luck and keep it up. The picture is great.