Royal Purple Max Gear 75/90 is a real good oil.

I wonder what makes the Redline foam up. Seems like they'd know it and do something about it...???

To each and all their own choices. I spend my money on AMSOIL for the drives. Not huge power. Lot's of people around here use it. Twin Bravos.

I use Amsoil. Never had any problems.

I had my drive upgraded at Teague Custom Marine and they recommend the Amsoil. So, I go with the pros.

Ive heard you can pick up 1-2 mph speed increase when switching from Merc to Amsoil. anybody see this?

I don't have a gps, I ran 70 with 120# gf and 20 gallons fuel, best with this drive is 73 speedo with 10 gallons just me. When I burn some fuel off I'll go out alone and see if I picked up anything. Skater buddy says 1 or 2 also.