jeebus cripes, the bike isnt exactly powerful. there's no need to play with the throttle unless you're a pussy or you have no self control in which case you probably shouldnt even be riding a bicycle.
start in 250..if you are absolute new..see the crash analysis post of a guy crashed near dumbarton .. if you are not familiar with what you are doing..it could be disastrous..moreover a 650 to start with is heavy for your size.. i guess its around 360-370lbs..