So much material, so little time.
First you could buy a Suzuki
Second if you are all on 125 cc bikes I believe the best way to be faster then the rest is to be a better rider then the rest. Speed is usless unless you can control it.
Third the quick fix is to change sprockets gear the bike up for quicker acceleration unless this is a top speed contest then gear it down.
I highly recomend the first option the most.