A lot of it is going to depend on the TDS
of your tap water normally. If you live in a low to mid-low TDS
area, it's not going to be that big of a deal using the 125 gpd membrane. (Remember, using the same water pressure, a 80 gpd membrane or a 100 gpd membrane will remove more contaminants).
You also have to consider the cost....that thing is dirt cheap.