[Knot On Call]

I spoke with Tiara and Michigan Wheel on 3 vs 4 blade. 3 blade is theoretically more efficient. 4 blade may be a little smoother. I was debating going from 3 to 4 blade on my 2003 52 Sovran Salon. With a purchase cost of (2) 4 -blade props near $10K, the money could be put to better use (like in my pocket). As long as the prop is giving you 97-98% load at WOT and you hitting the max RPMs, you are props are properly speced. Remember, higher air temps and warmer water will definitely affect performance negatively, so stay conservative in cooler weather sea trials, otherwise you can overload your engines and may find overload alarms going off mid-summer. Older boats definitely get heavier so original specs may not apply to the boat anymore espially if you load it up with fuel, water, refreshments, and people. I had to reduce my original pitch from 40 to 39 to keep within performance ranges. Michigan Wheel tech service is a good source to review your performance. They have work sheets to submit with RPM, engine load, and speed. They will also recommend any changes.
I don't know if props will affect your altitude running characteristics significantly. It could be just the boat. My boat runs higher than I would prefer. I use the trim tabs. Still if place the bow too low I will lose speed. It just likes to run a little high most efficiently. Mike