Another reason not to use 28T rear sprocket freewheel: Ground clearance.

Below image is a 23T rear sprocket with added chain links (added weight).
Lower pulley of the rear derailleur is about 1" off the ground.

Using a larger rear sprocket would require longer chain (add more weight) to avoid the lower pulley dragging on the ground while riding.. or just go with a shorter cage rear derailleur to maximize ground clearance.



BTW, swapped out the B/B and cranks to Rival alloy/Red carbon crankarms and EXO B/B for additional weight saving.