[Water Warrior 2]

A little further thought has lead me to think you wouldn't like the change. Flat ground or not you might be in 4th gear more than 5th. The GZ just doesn't have the power to pull a 16/38 gearing. You are asking the bike to do something it was never meant to do.
Likely you will need a new longer chain too so the investment will be a costly experiment if it doesn't work.