Think about it this way.
How many years of warranty till you might have to worry about a problem?

Did some looking this weekend. Options are Optimax 150, Yam F150, suzuki 150 or 175. The age old question about 2 stroke vs 4 stroke? What is the advantage of 4 over 2? Why not a 2 cycle?
How do they stack up:
- Price per Hp
- Weight per HP
- Performance Hp to HP
It seems the 2 cycle still is better in these categories.
???

Something I would consider is number of dealers and popularity of a particular brand in your area.

Weight is an issue with our older boats too.

Can't go wrong with Evinrude or Merc because parts and service is so readily available.

Believe Merc Opti may sqeeze out the most fuel economy, but more noise than the Rude.

If low 40's mph is enough for you, go with the 150hp, less weight, very good fuel economy and you should be very happy.