I have the 4 stroke 150 and run 87 Octane all the time (with ethanol). I use Yamaha ringfree all the time and in the winter I use Stabil since the boat sits for about 30 days at a time. Never had any issues yet with 950 hours on the motor.
They have a product down here at marinas and gas stations and throughout the Keys called recreational vehicle fuel or Rec Fuel. Essentially it's ethanal free 90 octane. Just got some at a Sunoco gas station $4.25 gal.