For the "average" boater there is a very limited benefit to going with a stainless prop (which is often 2 to 3 times the cost of aluminum).
While it is true that stainless flexes less than aluminum or composite we are talking about a relatively low powered motor here (only 50 horses).
The "less flex" will make it "bite" the water a little harder, but add to the "slip" that all props experience. So in all probability, on this particular motor, if your current pitch/diameter is correct then you should prop with exactly the same pitch/diameter in stainless.
Unless you are running is salt water (which will corrode an aluminum prop), it's my opinion that you would be better served putting your money somewhere else besides a stainless prop which would give you "no noticeable" performance benefit and will lighten your wallet considerably.
If you are not correctly propped (can only tell with a tach), then simply getting a suitable pitch/diameter prop in either aluminum, an alloy or a composite would make far more difference the overall performance, making a switch to stainless practically un-necessary..