I would think the 16x15 would be sufficient. I run the 16x17 now and all 100% full ballast+ 500 lbs lead distributed evenly side to side + crew of 4-5 adults and I have not experienced any lag pulling a surfer. 400 engine. I thought it would be necessary to go down to 16x15 but have not been hurting for it. I do plan to get a second prop and it'll be 16x15 but frankly, not out of necessity. Just my 2 cents.
I just cant imagine what I'm gaining by moving down to a 13"pitch. Loose speed, increased RPM. Considering how my boat handles it now, I just don't see the payoff for what I'd be giving up.