get some knobbly tires and hit the dirt bike track! i think a lot of people will agree that dirt riding is harder then street track riding. although their are some aspects of street track riding that is easier on the dirt.
all in all their are no speed limits on the dirt track, if u fall u minimize the chance of getting seriously hurt as the dirt gives a little more cushion then asphalt, and ur bike won't get too banged up if u fall!
the body positioning is similar in the dirt but not directly related, but i beleive u have a easier time learing to move from the dirt to the street then u do from the street to the dirt. so if u learn to ride fast in the dirt then u should have a particularly easy time transfering over to the street track. 
plus i think the dirt track is a little cheaper per practice day then a street track!
1993 Cr500r
educatio est omnium efficacissima forma rebellionis!
levels of insaity:
1 - talks to self 2 - argues with self 3 - loses argument with self 4 - is no longer speaking to self