yup.. u can search for a video in youtube where this turkish dude did 170kmh on his zzr 250...
btw, if u are light i think the bike can reach 180kmh...
my personal record though is 190kmh -> dont know if my meter is accurate or not but what the heck 
the speedo on the lc varies..
theres this one lc that i overtook @ 100kmh but suprisingly when i took a peek at his speedo i can see that the needle pointing to 130kmh already..
but another instance when i overtook another lc @ 100kmh, i can see that his meter showed 120 kmh only..
and some US bikers has tested that the zzr 250 meter is off by 20kmh compared to the reading given by GPS.. 
so.. the true speed for lc is speedo - 50 or 40... 
wow, u mod ur engine, carb, piping but u forgot something, good rubber...
viva tyre arent very good bro, they dont give enough grip.. and if u try to take a corner at highspeed.. then it'll likely lose traction and cause u to low slide..
btw i really suggest u try, michelin pilot sport or if u're feeling rich try the bridgestone battlax bt 090  ...
or bt 39ss <- cup prix tyre