one of my friend is above 100kg and he is happily cruising his hero 72cc (69cc) since 2006 till to date. his daily ride is almost 35 km since 2008.. in between (few years back) he spent 4k and rebuild the engine with chinese parts and is paddling happily on it.
his bike is hero rf 70.
it is pertinent to mention that we used it for double sawari for a year or so. my weight being 70kg.
so even a 70 with 78cc labelled cylider engine will be ok. (i am using dhoom 2009 model and its runing great and i have abused it a lot . had opened its engine for all sort of experimentation .. ) other good 70cc chondas are uniqe.hero.united.superpower. for 70cc i would advise you to stay away from honda cd 70.. you being a banker could justify the resale myth of honda ..
a 100cc is a good balance between power and economy .(buy honda cd 100.. or some chonda 100)
a 125 will be luxury
consider avg of chonda 70 to be 50-55 at most in real circumstances. and that of honda 125 to be 35-40 at best. so if you ride a lot of kms daily then a 70 will help save some petroRupees. however if its little ride like hardly 15-20 kms both side then 125 is good
my few paisas of advise for free