well i may not be a pro commuter but if i were you id look at convertin a mtb into a sort utilitarian bike im 6 foot 6 and around 250 lbs so i know that the difrence between a 5 lb and a 15 lb frame is almost nothing. althoguh i havent used the exspensive bikes id assume theres not a ton of diffrence.

i am about to get a bunch of beaters and try to build a utilitarian bike like the "trek t80" its about 600 dollars out of my price range being almost 700 dollars. i make it to work just fine on my 100 dollar mtn bike but i want to make it a little more comfortable for me to carry stuff on. and just rinde in general

oh almost forgot the most important thing
get a mtn bike but put slicks on it for tires the nubbies will sap your energy