[Milwaukee M18 double cut metal shear, in 14ga or 18ga cutting ability.]

My concern is, will the 14ga do everything the 18ga will do plus on thicker metal?  Cutting over roofing ridges works with the 18, seen it used.  Would it work as well with the 14?

 

[Milwaukee M18 double cut metal shear, in 14ga or 18ga cutting ability.]

Hi, Considering the Milwaukee M18 double cut metal shears and they come in 14ga and 8ga cutting ability.  Hobbyist, retired.  Putting a metal roof on right now.  The 18ga would handle the roofing but would I be smarter spending the extra $20 to get the 14ga?  Thanks!