Re: Aluminum or SS 3 or 4 blade
IMO, If you put a 19" 3 blade SS prop on, you will lose RPM. They are heavier, & more rigid then aluminum. You probably should drop down to a 17" 3 blade SS to keep the rpm's up, maybe a 17", or 18" SS 4blade would work, it definitely would give you more power out of the hole, & for extra loads, but you may scrub some speed.
A SS prop has more of a solid feel, it feels more stable, and has more thrust at all speeds. It also holds it's speed setting better the aluminum, regardless of sea conditions, it almost feels like cruise control. Each time you hit the throttle, there will be an instant jolt of power, no soggy, or soft feelings like aluminum. The bottom line is, it's more efficient! But, it takes more power to spin it then an aluminum prop.