For what its worth.... I had a 32 foot cruiser w/ twin inboards (Mopar 360s). Port prop was a 16 x 16 with minimal cup. Starboard prop (a replacement after an ooops!) was a 16 x 15. so I took it to a prop shop to get an inch of pitch added. "No can do," the man told me, but he hammered a heavy cup on the three blades.

Both engines ran identically, with rpm and hole shot similar--I did extensive testing. So 16 x 16 mild cup equals 16 x 15 heavy cup.

Jeff