for 125z get the original sprocket.. its called original for a reason and its set to that speed for a reason..if u wanna modify untill fly 150-200.. stay off the road or get a better bike. if u wanna rempit go aim at the wall or aim go under the lorry let them kill u before u kill someone else..

but if u wan typically built for speed not pick up heres a no brainer. smaller front sprocket with bigger rear ones should get the job done.
my previous TZM using 14-42 pickup kinda slow but still ok and top speed is reasonable.
now using CBR so not so sure.
for taking motorcycle test without hand signal i think i knnow one near inti collage nilai... i took my b full there and i see those b2 fella never use hand also.